Merkel Cell Carcinoma
Merkel cell polyomavirus-associated neuroendocrine skin cancer
DefinitionClick to collapse
Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous neuroendocrine neoplasia. It arises from Merkel cells, which are touch-sensitive neuroendocrine cells in the skin. MCC is characterized by small round cells with sparse cytoplasm, abundant mitoses, and dense core granules on histology [61,93,95,124,155]. Clinically, MCC presents as a rapidly growing, often asymptomatic, red or purple nodule on sun-exposed skin. In a study of 195 patients, 63% of primary lesions had grown rapidly in the three months prior to diagnosis, and correct clinical diagnosis was rare (1%) [7]. MCC can metastasize early, with 63% of primary lesions having grown rapidly in the 3 months prior to diagnosis [7]. Large meta-analyses show that at least half of patients develop lymph node metastases and nearly one third develop distant metastases [8-15]. MCC has a high mortality rate, exceeding melanoma, with 5-year relative or MCC-specific survival rates ranging from 41% to 77% depending on stage at presentation [2,10,13,18-23]. The definitive diagnosis relies on immunohistochemistry (IHC): cytokeratin 20 (CK20) positivity (membranous and/or paranuclear dot-like) and thyroid transcription factor 1 (TTF-1) negativity are usually sufficient [5,6,93,160,162-165]. Additional neuroendocrine markers (e.g., synaptophysin, neurofilament, INSM1, chromogranin) may be used [29,75,80,93,95,160,161,166-173]. MCC is distinct from metastatic small cell lung carcinoma (SCLC) by IHC. The disease can be categorized by clinical presentation: local disease (clinical N0), regional disease (clinical N+, including in-transit disease), and distant metastatic disease (M1). The AJCC 8th edition staging system is used, with T stage based on tumor size and invasion, N stage based on nodal and in-transit metastases, and M stage based on distant metastases [12,66]. The NCCN guidelines emphasize multidisciplinary consultation at a center with specialized expertise for optimal management [MCC-1].
EpidemiologyClick to collapse
SubtypesClick to collapse
MCPyV-Positive Merkel Cell Carcinoma
MCC tumors that harbor Merkel cell polyomavirus (MCPyV) DNA, detected in 43% to 100% of cases depending on the cohort [51-56]. These tumors typically have a lower mutational burden and are less associated with UV damage signatures. They are more common in immunocompetent individuals and may have a better prognosis compared to virus-negative tumors in some studies [57-60]. The viral oncoproteins (large T antigen) are expressed and can be targeted by immunotherapy.
MCPyV-Negative Merkel Cell Carcinoma
MCC tumors that are negative for MCPyV. They have a much higher mutational burden, enriched for cytosine to thymine (C to T) mutations indicative of UV damage [63-65]. They tend to occur more often on the head, neck, or trunk. MCPyV-negative status has been associated with increased recurrence [55] and decreased MCC-specific survival and overall survival in some studies [57-60], although not all studies confirm this [61,62]. These tumors may harbor mutations in TP53, RB1, and other genes.
Combined Merkel Cell Carcinoma
MCC tumors that are admixed or adjacent to other cutaneous malignancies, most commonly squamous cell carcinoma (SCC), but also basal cell carcinoma, melanoma, actinic keratosis, and Bowen disease [29-32,61,85,92,105-113]. The combined phenotype may have distinct clinical behavior; some studies suggest a higher likelihood of metastasis, disease progression, and death from disease [32].
Unknown Primary Merkel Cell Carcinoma
MCC presenting with nodal or distant metastases without an identifiable primary cutaneous lesion. These patients have a better outcome compared to those with synchronous known primary in some studies [12,41,175-178]. The NCCN recommendations for pathologic evaluation and management of the nodal basin are the same as for known primary disease [MCC-4].
Molecular PathogenesisClick to collapse
Merkel cell carcinoma (MCC) is driven by two distinct molecular pathways: one associated with Merkel cell polyomavirus (MCPyV) and another associated with UV-induced mutagenesis. MCPyV is a double-stranded DNA virus that is clonally integrated into the tumor genome in a significant proportion of MCCs, detected in 43% to 100% of cases depending on the cohort [51-56]. The virus expresses large T antigen (LT) and small T antigen (sT) oncoproteins that inactivate tumor suppressors, including retinoblastoma protein (RB1), and promote cell cycle progression [51]. In MCPyV-positive MCC, the viral oncoproteins are essential for tumor maintenance, and the tumors typically have a low mutational burden. In contrast, MCPyV-negative MCC arises from chronic UV exposure, accumulating a high burden of somatic mutations with a characteristic UV signature (C to T transitions) [63-65]. These tumors frequently harbor mutations in TP53, RB1, and other genes such as PIK3CA, PTEN, and those involved in chromatin remodeling [63-65]. Genomic analyses have shown that MCPyV-negative MCC have a significantly higher tumor mutation burden (TMB) compared to MCPyV-positive tumors [23]. Additionally, copy number alterations and chromosomal abnormalities are more common in MCPyV-negative tumors. Other molecular alterations include overexpression of survivin and mutations in PDGFRΞ± [53]. The expression of programmed death-ligand 1 (PD-L1) is frequently observed in MCC and may contribute to immune evasion. Immunohistochemical markers such as CK20, TTF-1, and neuroendocrine markers (synaptophysin, INSM1, chromogranin) are used for diagnosis [MCC-A]. The molecular classification has therapeutic implications: immunotherapy with PD-1/PD-L1 inhibitors is effective across both subtypes, but MCPyV-negative tumors may have a higher likelihood of response due to higher TMB and neoantigen burden. The NCCN guidelines note that in the Stage IV setting, next-generation sequencing (NGS) of the tumor can sometimes reveal relevant and actionable therapeutic targets [MCC-D 4 of 5], [23].
Risk FactorsClick to collapse
Ultraviolet (UV) Radiation Exposure
Strong evidence implicates sun exposure as a major risk factor, based on increased incidence in geographic areas with higher UV indices, tendency to occur on sun-exposed skin, and frequency of MCC being admixed or adjacent to UV-induced skin lesions [26-32].
Immunosuppression
MCC is disproportionally more common in immunosuppressed individuals, including solid organ transplant recipients, patients with chronic lymphocytic leukemia (CLL), HIV/AIDS, and those on chronic immunosuppressive therapy [7,33-39]. Immunosuppression is also associated with worse MCC-specific survival [19,38,40-47].
Age
MCC incidence increases with age, with the median age at diagnosis around 70 years [4,7,8,13,19]. The aging population contributes to rising incidence.
White Race
MCC is more likely to occur in white individuals compared to other ethnicities [4,7,8,13,19].
Merkel Cell Polyomavirus (MCPyV) Infection
MCPyV is detected in 43% to 100% of MCC tumors and is thought to be etiologic in virus-positive cases [51-56]. However, virus-negative tumors have a distinct molecular pathogenesis driven by UV. MCPyV seropositivity is common in the general population, so infection alone is not sufficient.
Germline Mutations in Cancer-Associated Genes
In patients under 50 years of age with MCC, germline mutations in known cancer-associated genes have been reported in approximately 20% [116]. Genetic counseling should be considered for these patients [MCC-1].
Male Sex
MCC incidence is slightly higher in males than females [1,4,8]. Some studies suggest worse outcomes in males, but not consistently.
Clinical FeaturesClick to collapse
Typical Presentation
Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous neuroendocrine neoplasm that typically presents as a rapidly growing, asymptomatic nodule on sun-exposed skin of the head/neck or extremities [7]. In a landmark study of 195 patients, 88% of MCC tumors were asymptomatic and correct clinical diagnosis was made in only 1% of cases; 56% were initially presumed to be benign cysts or lesions [7]. The lesion is often described as firm, dome-shaped, red-to-purple, with a smooth, shiny surface, sometimes with overlying telangiectasias [19,22]. Rapid growth is a hallmark: 63% of primary lesions had grown rapidly in the 3 months prior to diagnosis [7]. MCC carries a high mortality rate, with 5-year relative or MCC-specific survival ranging from 41% to 77% depending on stage at presentation [2,10,13,18-23]. At least half of patients develop lymph node metastases, and nearly one third develop distant metastases [8-15]. MCC incidence is increasing, with approximately 2488 new cases per year in the United States [1].
Symptoms
Asymptomatic nodule
Most MCC tumors are asymptomatic; the patient or clinician notices a new or changing growth with no associated pain, tenderness, or pruritus in the majority of cases [7].
Rapid growth
Primary lesion often grows rapidly over weeks to months. Patients may report a lesion that has noticeably enlarged in the prior 3 months [7].
Occasional pruritus, bleeding, or ulceration
Less common symptoms include itching, bleeding, or ulceration of the lesion, especially with larger tumors [7,19].
Signs
Firm, dome-shaped, red-to-purple nodule
Classic appearance: a smooth, shiny, dome-shaped nodule with a reddish or violaceous color, often with telangiectasias. May resemble a cyst, pyogenic granuloma, or basal cell carcinoma [7,19].
Lymphadenopathy
Palpable regional lymph node involvement at presentation is common. Large meta-analyses show at least half of patients develop lymph node metastases [8-15].
In-transit metastases
Cutaneous or subcutaneous nodules between the primary tumor and the draining nodal basin, may be palpable or visible [12,66].
Red FlagsClick to collapse
Rapidly growing nodule on sun-exposed skin (especially head/neck, extremities) with a latency of weeks to months [7].
Firm, red-to-purple dome-shaped nodule with telangiectasias, particularly >1 cm in diameter [19,22].
Presence of immunosuppression: solid organ transplant, chronic lymphocytic leukemia, HIV, or other causes of chronic T-cell immunosuppression [33-39].
Age >50 years; incidence increases with age, with most patients older than 65 [4,7,8,13,19].
History of prior or concurrent non-melanoma skin cancer, melanoma, or other cancers (MCC patients have increased risk of second primary malignancies) [19,23,35,91,94,97-104].
Palpable lymphadenopathy or in-transit nodules in the drainage basin of a suspicious skin lesion [12,66].
History of extensive sun exposure or residence in high UV index regions [26-32].
Positive sentinel lymph node biopsy or imaging evidence of occult nodal/distant metastases discovered during staging [19,50,83].
Rising serum Merkel cell polyomavirus (MCPyV) oncoprotein antibody titers (in seropositive patients) or new appearance of ctDNA positivity [55,122].
MCC diagnosed in patients <50 years of age (germline mutations in cancer-associated genes found in ~20%) [116].
InvestigationsClick to collapse
Diagnostic
Punch, shave, or excisional biopsy of suspicious skin lesion
Initial tissue diagnosis with adequate sampling [MCC-1].
Immunohistochemistry panel (mandatory)
To distinguish MCC from other small round cell tumors, especially metastatic small cell lung cancer [MCC-A].
Sentinel lymph node biopsy (SLNB) with appropriate immunopanel
Most reliable tool to identify subclinical nodal disease. Should be performed prior to or at time of definitive excision [MCC-2, MCC-C].
Fine-needle aspiration or core biopsy of palpable lymph nodes
Confirmation of nodal involvement in clinically N+ disease [MCC-4].
Excisional biopsy of lymph node (if FNA/core negative but high suspicion)
Confirm negative initial biopsy if clinical suspicion remains high [MCC-4].
Staging
Complete skin and lymph node examination
Full skin inspection and palpation of all nodal basins to detect primary, in-transit, nodal, or distant cutaneous metastases [MCC-1].
Whole-body FDG-PET/CT (preferred) or CT with contrast of chest/abdomen/pelvis (plus neck if primary on head/neck, and brain MRI if clinical suspicion of brain metastases)
Imaging for staging of most MCC; occult metastatic disease detected in 12-20% of patients without suspicious H&P findings [151]. FDG-PET/CT has high sensitivity (90%) and specificity (98%) per meta-analysis [140]. May also help rule out skin metastasis from non-cutaneous primary neuroendocrine carcinoma (e.g., SCLC) [MCC-1].
Sentinel lymph node biopsy (SLNB)
Gold standard for staging the nodal basin in clinically N0 disease; impacts regional control and provides prognostic information [MCC-2, MCC-C].
CT or MRI of brain with and without contrast
Best imaging tool for rare MCC brain metastases, though most Panel members reserve for patients with neurological symptoms or widespread systemic disease [148-150,152].
Somatostatin receptor scintigraphy or PET (e.g., 68Ga-DOTATATE)
Optional; may identify somatostatin receptor-expressing metastases for potential octreotide therapy [MCC-D, 317].
Biomarkers
Merkel cell polyomavirus (MCPyV) oncoprotein antibody testing
Prognostic and surveillance tool. Seronegative at diagnosis associated with higher recurrence risk. Seropositive patients with rising titers may have early recurrence [55,56,117-119].
Circulating tumor DNA (ctDNA) testing (tissue-informed)
Assesses disease burden in both virus-positive and virus-negative MCC; becomes positive prior to or at time of clinically evident recurrence [122].
Genetic counseling for germline mutations in cancer-associated genes
Mutations found in ~20% of patients <50 years of age [116].
StagingClick to collapse
AJCC 8th edition (2017) TNM staging system for Merkel cell carcinoma [12,66]
T Categories
| Stage | Description |
|---|---|
| TX | Primary tumor cannot be assessed (e.g., curetted) |
| T0 | No evidence of primary tumor |
| Tis | In situ primary tumor |
| T1 | Maximum clinical tumor diameter β€2 cm |
| T2 | Maximum clinical tumor diameter >2 cm but β€5 cm |
| T3 | Maximum clinical tumor diameter >5 cm |
| T4 | Primary tumor invades fascia, muscle, cartilage, or bone (extracutaneous extension) |
N Categories
| Stage | Description |
|---|---|
| NX (clinical) | Regional lymph nodes cannot be clinically assessed (e.g., previously removed for another reason, or because of body habitus) |
| N0 (clinical) | No regional lymph node metastasis detected on clinical and/or radiologic examination |
| N1 (clinical) | Metastasis in regional lymph node(s) |
| N2 (clinical) | In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) without lymph node metastasis |
| N3 (clinical) | In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) with lymph node metastasis |
| pNX | Regional lymph nodes cannot be assessed (e.g., previously removed for another reason or not removed for pathological evaluation) |
| pN0 | No regional lymph node metastasis detected on pathological evaluation |
| pN1 | Metastasis in regional lymph node(s). Subcategories: pN1a(sn) = clinically occult metastasis identified only by sentinel lymph node biopsy; pN1a = clinically occult metastasis following lymph node dissection; pN1b = clinically and/or radiologically detected metastasis, microscopically confirmed |
| pN2 | In-transit metastasis without lymph node metastasis |
| pN3 | In-transit metastasis with lymph node metastasis |
M Categories
| Stage | Description |
|---|---|
| M0 | No distant metastasis detected on clinical and/or radiologic examination |
| M1 | Distant metastasis detected on clinical and/or radiologic examination. Subcategories: M1a = metastasis to distant skin, distant subcutaneous tissue, or distant lymph node(s); M1b = metastasis to lung; M1c = metastasis to all other visceral sites |
| pM1 | Distant metastasis microscopically confirmed (with same subcategories: pM1a, pM1b, pM1c) |
Stage Groupings
| Group | Criteria | Clinical Meaning | Five Yr Survival | Treatment Intent |
|---|---|---|---|---|
| Stage 0 (clinical and pathological) | Tis N0 M0 | In situ disease, no nodal or distant involvement | Not specified separately; overall survival for MCC varies from 41-77% by stage [2,10,13,18-23] | Curative β local excision with margin assessment |
| Stage I (clinical and pathological) | T1 N0 M0 | Small primary tumor (β€2 cm), no nodal or distant disease | 5-year relative survival approximately 75-80% (estimated from NCDB data [12]) | Curative β surgery (excision + SLNB) Β± adjuvant RT if risk factors |
| Stage IIA (clinical and pathological) | T2-T3 N0 M0 | Primary tumor >2 cm but β€5 cm (T2) or >5 cm (T3), no nodal or distant disease | 5-year relative survival approximately 60-70% (estimated [12]) | Curative β surgery + adjuvant RT often indicated due to higher risk features |
| Stage IIB (clinical and pathological) | T4 N0 M0 | Primary tumor invades fascia, muscle, cartilage, or bone; no nodal or distant disease | 5-year relative survival approximately 50-60% (estimated [12]) | Curative β surgery + adjuvant RT; may require multidisciplinary approach |
| Stage III (clinical) | Any T (T0-T4) N1-3 M0 | Regional nodal involvement (N1-3) without distant metastases; includes in-transit disease [12,66] | 5-year survival approximately 40-50% (estimated from NCDB [12,79]) | Curative β node dissection + RT preferred; systemic therapy may be considered |
| Stage IIIA (pathological) | T1-T4 N1a(sn) or N1a M0; or T0 N1b M0 | Clinically occult nodal metastasis (identified by SLNB or LND) or nodal metastasis from unknown primary with microscopic confirmation | 5-year survival approximately 50-60% (estimated [12]) | Curative β surgery (node dissection or RT) Β± systemic therapy (clinical trial preferred) |
| Stage IIIB (pathological) | T1-T4 N1b-3 M0 | Clinically detected nodal metastasis (N1b), in-transit with or without nodal involvement (N2-N3) | 5-year survival approximately 30-40% (estimated [12]) | Curative intent but high risk β node dissection + RT preferred; strong consideration of systemic therapy/clinical trial |
| Stage IV (clinical and pathological) | Any T (T0-T4), any N (N0-3), M1 | Distant metastases (skin, subcutaneous tissue, lymph nodes, lung, other visceral sites) | 5-year survival approximately 15-25% (estimated from studies [13,18-23]) | Palliative β systemic therapy (immunotherapy preferred), RT, surgery for oligometastases, best supportive care |
Staging Pearls
- Clinical N0 disease requires SLNB for accurate pathological staging; false-negative SLNB occurs in 5-12% of cases [46,50,180].
- In-transit metastasis (N2/N3) is defined as discontinuous from primary tumor, located between primary tumor and draining nodal basin or distal to primary tumor [12,66].
- Pathological staging (pN) refines nodal categories with subcategories pN1a(sn), pN1a, pN1b based on method of detection and clinical presentation.
- M-stage subcategories M1a, M1b, M1c have prognostic significance; brain metastases are rare but MRI indicated when clinical suspicion [148-150].
- Patients with unknown primary MCC (T0 N1b M0) have better prognosis than those with synchronous known primary [12,41,175-178].
- The AJCC 8th edition is based on analysis of 9387 patients from NCDB with median follow-up 28.2 months [12].
- Tumor thickness (Breslow, mm) is strongly encouraged to report but is not part of T staging; it correlates with SLN positivity and survival [49,76,83-85].
- Stage IIA includes T2 and T3 tumors; outcomes for T2 vs T3 may differ but grouped due to similar survival curves [10,12].
Management PrinciplesClick to collapse
Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous neuroendocrine malignancy requiring a multidisciplinary, multimodal approach to optimize outcomes. The treatment philosophy centers on accurate staging, complete surgical resection when feasible, and judicious use of adjuvant or definitive radiation therapy (RT) and systemic therapy, particularly immune checkpoint inhibitors. Given the high propensity for locoregional recurrence and distant metastasis, the NCCN Panel strongly recommends multidisciplinary consultation at a center with specialized expertise for all stages of disease (MCC-1, MCC-3, MCC-4, MCC-5) [1-3]. Immunosuppression is a key risk factor for poor outcomes; therefore, immunosuppressive treatments should be minimized as clinically feasible, and more frequent follow-up is indicated for immunocompromised patients (MCC-1) [4,5]. For patients younger than 50 years, genetic counseling to evaluate for germline mutations in cancer-associated genes is recommended, as such mutations are reported in approximately 20% of this age group (MCC-1) [6]. The overall treatment plan integrates surgery, RT, and systemic therapy based on clinical and pathologic stage, resectability, patient fitness, and tumor biology.
Curative intent for localized disease
Clinical N0, local MCC only, surgically resectable
Primary treatment consists of surgical excision with 1β2 cm margins (or Mohs/PDEMA in selected circumstances) plus sentinel lymph node biopsy (SLNB). For microscopically positive margins, adjuvant RT is preferred over re-excision. For SLN-negative patients with no adverse risk factors, observation is sufficient; with one or more adverse risk factors (LVI, immunosuppression, tumor >1 cm, close/positive margins, positive SLNB, head/neck site), adjuvant RT to the primary site is recommended (category 2A). For SLN-positive patients, baseline imaging is obtained, and additional treatment includes RT to the nodal basin, node dissection, or both. Node dissection with adjuvant RT is indicated for multiple involved nodes or extranodal extension (MCC-2, MCC-2A) [7-9].
Curative intent for locally advanced disease not amenable to upfront surgery/RT
Clinical N0, locally advanced MCC when curative surgery and RT are not feasible
Multidisciplinary consultation is required. For surgical candidates, neoadjuvant nivolumab may be considered (category 2A, useful in certain circumstances). After neoadjuvant therapy, adequate responders proceed to excision and SLNB per resectable pathway; those with progression are offered RT or surgery for local control versus systemic therapy. For nonsurgical candidates (due to comorbidities or tumor characteristics), discussion of RT for durable local control versus systemic therapy is recommended (MCC-3) [10].
Curative intent for regional disease
Clinical N+ (regional MCC/in-transit) without distant metastases
Management of the draining nodal basin in N+ disease: preferred treatment is node dissection plus RT. Alternative options include node dissection alone, RT alone, clinical trial, or consideration of systemic therapy. For in-transit disease, biopsy confirmation is followed by clinical trial, surgery, RT, systemic therapy, or additional local considerations (T-VEC, hyperthermic isolated limb infusion/perfusion) if curative surgery/RT not feasible (MCC-4) [11,12].
Palliative intent for metastatic disease
M1 disseminated MCC
Multidisciplinary consultation at specialized center. Clinical trial preferred. Treatment options include systemic therapy (PD-1/PD-L1 inhibitors preferred), RT for symptom control, and surgery for limited metastases in highly selective circumstances. Best supportive care is always appropriate (MCC-5) [13].
Treatment of recurrence
Any recurrence (local, regional, in-transit, disseminated)
Follow-up every 3β6 months for 3 years, then every 6β12 months. For local/regional recurrence: clinical trial, systemic therapy, RT, surgery, or best supportive care. In-transit recurrence: manage per in-transit pathway. Disseminated recurrence: treat as M1 disease. Serum MCPyV oncoprotein antibody and ctDNA surveillance every 3 months may aid early detection (MCC-6) [14,15].
Multidisciplinary consultation at a center with specialized expertise is recommended for all patients at initial workup (MCC-1) and for those with locally advanced disease (MCC-3), clinical N+ disease (MCC-4), and M1 disease (MCC-5). The team should include dermatologists, surgical oncologists, radiation oncologists, medical oncologists, pathologists, and radiologists experienced in MCC management. This collaboration ensures appropriate staging, treatment sequencing, and consideration of clinical trials.
The NCCN guideline does not provide a specific performance status (PS) scale or score for treatment selection. However, PS is implicitly considered when determining surgical candidacy. For nonsurgical candidates due to comorbidities, definitive RT or systemic therapy is discussed. For patients with M1 disease, best supportive care is an option regardless of PS. The decision to use systemic therapy, especially immunotherapy, should balance potential benefit with the risk of immune-related adverse events. Clinician and patient education on immunotherapy toxicities is critical (MCC-D 1 of 5) [16].
Management PathwaysClick to collapse
Branching: SLN status (positive or negative), margin status (clear, microscopically positive, grossly positive), presence of adverse risk factors (LVI, immunosuppression, tumor >1 cm, close/positive margins, positive SLNB, head/neck site)
Branching: Surgical candidacy, Response to neoadjuvant nivolumab
Branching: Nodal basin biopsy result (positive or negative), Presence of distant metastases (M0 vs. M1), In-transit disease
Branching: Metastatic site and burden, Patient fitness and preference
Branching: Type of recurrence (local, locally advanced, regional, in-transit, disseminated)
Pretreatment EvaluationClick to collapse
Clinical assessment
Imaging studies
Laboratory studies
Pathology and biopsy
Genetic and immunosuppression assessment
SurgeryClick to collapse
Surgery is the primary treatment modality for most MCC and is required for accurate pathological staging of both the primary lesion and regional disease. The goals are to obtain histologically negative margins when clinically feasible while balancing morbidity, and to facilitate appropriate adjuvant therapy. Surgery includes excision of the primary tumor and sentinel lymph node biopsy (SLNB), with or without completion lymph node dissection depending on nodal status.
Obtain histologically negative margins when clinically feasible; surgical margins should be balanced with morbidity of surgery (MCC-C).
Coordinate surgical management so that SLNB is performed prior to or at the time of definitive excision, especially for head and neck primaries where prior resection/reconstruction may alter lymphatic drainage (MCC-C) [31].
If adjuvant RT is planned, narrow excision margins are likely sufficient; if adjuvant RT may not be indicated, perform wide excision with 1- to 2-cm margins to investing fascia of muscle or pericranium when clinically feasible and consistent with reconstruction and RT goals (MCC-C) [7].
Techniques for more exhaustive histologic margin assessment (Mohs or other forms of PDEMA) may be considered provided they do not interfere with SLNB; if SLNB not performed concurrently, perform SLNB prior to definitive excision (MCC-C) [32].
Reconstruction involving extensive undermining or tissue movement should be delayed until negative histologic margins are verified and SLNB performed if indicated. Closure should allow for expeditious initiation of RT (e.g., primary closure, avoiding extensive tissue movement) (MCC-C) [7].
Procedures
Wide local excision (WLE)
Primary MCC with clinically node-negative disease, especially if adjuvant RT is not planned. Also for primary tumor in regional disease setting.
Mohs micrographic surgery
Selected cases, especially in cosmetically sensitive areas or when tissue preservation is important. May achieve high local control rates. Requires coordination with SLNB timing.
Sentinel lymph node biopsy (SLNB)
All patients with clinically node-negative, surgically resectable MCC (category 2A). Important staging tool that impacts regional control for SLN-positive patients.
Lymph node dissection (LND)
Positive SLNB (especially if multiple nodes or ENE); clinically N+ disease confirmed by biopsy. Preferred combined with RT for high-risk features.
Radiation TherapyClick to collapse
Radiation therapy plays a critical role in both curative and palliative management of MCC. It is used as adjuvant therapy after surgery to reduce locoregional recurrence, as definitive treatment for patients who are not surgical candidates or refuse surgery, and for palliation of symptoms. The NCCN Panel emphasizes expeditious initiation of adjuvant RT after surgery as soon as wound healing permits, as delays >7β8 weeks are associated with worse outcomes (MCC-B 1 of 6) [33].
Principles
- Limited evidence supports dosing recommendations for MCC; dose ranges are based on clinical practice at NCCN Member Institutions and clinical evidence from other skin cancers (MCC-B 1 of 6).
- Recommendations for external beam RT (EBRT) apply to both photons and electrons.
- Image-guided radiation therapy (IGRT) is considered best practice when treating with IMRT, proton beam, or 3D conformal RT; IGRT for other skin cancer RT techniques is unnecessary (MCC-B 1 of 6).
- Application of bolus over the primary tumor should be considered to ensure full dose to the surface; surface dosimeters should be considered to verify delivered dose (MCC-B 1 of 6).
- Radiation treatments should be given by a practicing radiation oncologist with radiation physics support to meet quality assurance and dosimetric constraints (MCC-B 1 of 6).
- For primary tumor site, wide margins (5 cm) should be used when clinically feasible, with consideration of anatomic constraints (e.g., eye, mouth). If electron beam, energy and prescription isodose must ensure adequate dose to lateral and deep margins (MCC-B 2 of 6).
Dose Frameworks
| Name | Total Dose | Dose Per Fraction | Fractions | Schedule | Indication |
|---|---|---|---|---|---|
| Adjuvant RT to primary tumor β conventional fractionation | 50β56 Gy for negative margins; 56β60 Gy for microscopically positive margins; 60 Gy for grossly positive margins (if further resection not possible). | 1.8β2 Gy | 25β33 typically | Daily, 5 days/week | Postoperative RT for patients with β₯1 risk factors for local recurrence (LVI, immunosuppression, primary >1 cm, close/positive margins, positive SLNB, head/neck site). In subsets at high risk (e.g., chronic profound immune suppression), up to 66 Gy may be considered (MCC-B 2 of 6, MCC-B 3 of 6) [17]. |
| Adjuvant RT to primary tumor β hypofractionation | 44β50 Gy (2.2β2.5 Gy x 20 fractions); 30β35 Gy (3β3.5 Gy x 10 fractions); 8 Gy x 1 fraction (for selected low-risk patients). | 2.2β3.5 Gy; 8 Gy single fraction | 1β20 | Daily or as specified | Consider for patients who cannot tolerate conventional fractionation; avoid in patients at higher risk (e.g., immunosuppression) where data limited (MCC-B 2 of 6, MCC-B 3 of 6) [17]. |
| Definitive RT to primary tumor (clinically evident) β conventional fractionation | 56β60 Gy | 1.8β2 Gy | 28β33 | Daily | Unresectable tumor, surgery refused, or surgery would result in significant morbidity (MCC-B 2 of 6) [17]. |
| Definitive RT to primary tumor β hypofractionation | 50 Gy (2.5 Gy x 20); 45β51 Gy (3 Gy x 15β17); 40 Gy (4 Gy x 10); 30β35 Gy (6β7 Gy x 5, non-consecutive); 24 Gy (8 Gy x 3, non-consecutive). | 2.5β8 Gy | 3β20 | Daily or non-consecutive | Alternative for patients with limited access or comorbidities; caution with fractions >5 Gy/fraction when targets involve cartilage or bone (MCC-B 2 of 6, MCC-B 3 of 6) [17]. |
| Palliative RT to primary tumor or metastases | 30 Gy (3 Gy x 10); 20 Gy (4 Gy x 5); 8β24 Gy (8 Gy x 1β3 fractions). | 3β8 Gy | 1β10 | Daily or as tolerated | Symptom control; durable palliation likely higher with 8 Gy x 3 fractions (MCC-B 2 of 6, MCC-B 3 of 6) [17]. |
| Adjuvant RT to regional nodes β conventional fractionation | 50β56 Gy (SLNB without LND, SLN positive); 50β60 Gy (after LND with multiple involved nodes and/or ENE). | 1.8β2 Gy | 25β33 | Daily | For SLN-positive disease: RT to nodal basin if no dissection; after dissection for multiple nodes/ENE. RT to nodal basin may be considered in certain high-risk scenarios (compromised SLNB, high false-negative risk, profound immunosuppression) (MCC-B 4 of 6) [19,34]. |
| Definitive RT to regional nodes β conventional fractionation | 60 Gy (no SLNB or LND, clinically evident lymphadenopathy); 46β50 Gy (clinically node negative but at risk for subclinical disease). | 1.8β2 Gy | 23β33 | Daily | For patients with clinically evident nodal disease who are not candidates for LND, or for elective nodal irradiation (MCC-B 4 of 6) [20]. |
| Hypofractionation and palliative RT for regional nodes | Hypofractionation: 44β50 Gy (2.2β2.5 Gy x 20); 30β35 Gy (3β3.5 Gy x 10); 16 Gy (8 Gy x 2). Palliative: 30 Gy (3 Gy x 10); 20 Gy (4 Gy x 5); 8β24 Gy (8 Gy x 1β3). | 2.2β8 Gy | 1β20 | Daily or as specified with caution for lymphedema risk. | Hypofractionation for selected patients; palliative for symptom control. Use caution in patients with existing lymphedema or high risk (high BMI, groin basin, current smoker). Hypofractionation generally reserved for older patients or those unable to come for protracted course (MCC-B 4 of 6, MCC-B 5 of 6) [17]. |
Approaches
| Name | Dose Fractionation | Concurrent Chemotherapy | Indication | Key Trial | Toxicities |
|---|---|---|---|---|---|
| Adjuvant RT (postoperative) | Conventional fractionation (1.8β2 Gy/fx) as above for primary and nodal basins; hypofractionation alternatives. | Not routinely recommended. Data do not support routine use of concurrent chemoradiation; may be considered on case-by-case basis (e.g., positive margins, tumor β₯3 cm) but survival benefit not clearly established (MCC-D 3 of 5) [21,35]. | Patients with β₯1 risk factors for local recurrence; SLN-positive disease; positive margins; after node dissection for multiple nodes/ENE. | Multiple retrospective analyses and NCDB studies show improved locoregional control and survival with adjuvant RT in appropriate patients [7,19,20,33,35]. | Acute: dermatitis, fatigue, mucositis if head/neck. Late: fibrosis, lymphedema (especially nodal RT), secondary malignancy risk (small). |
| Definitive RT (without surgery) | Conventional fractionation 56β60 Gy (primary) or 60 Gy (nodes); hypofractionation options. | Not standard; concurrent chemotherapy not supported by high-level evidence. | Patients with unresectable disease, medical inoperability, or refusal of surgery. May provide good local control. | Retrospective data: SEER analysis showed improved OS and DSS with RT alone vs. no treatment in non-surgical patients. In-field recurrence after definitive RT ~12% per site [20,36]. | Similar to adjuvant RT; higher doses may increase late effects. |
| Palliative RT | Various hypofractionated schedules (e.g., 8 Gy x 1, 20 Gy/5 fx, 30 Gy/10 fx). | Not typically used; may be combined with systemic therapy in selected cases. | Symptomatic metastases (bone pain, bleeding, obstruction, brain metastases). Durable palliation better with higher dose regimens (8 Gy x 3). | No dedicated MCC trials; extrapolated from palliative RT for other solid tumors. | Generally well tolerated; acute fatigue, skin reaction, depending on site. |
Systemic TherapyClick to collapse
Systemic therapy for MCC has evolved significantly with the advent of immune checkpoint inhibitors (ICIs). Non-randomized trials demonstrate that rates of durable response are improved with PD-1/PD-L1 blockade compared with cytotoxic therapy, and safety profiles differ substantially. Chemotherapy, while associated with response rates of 40β60%, tends to have short durations and higher toxicity. The NCCN Panel emphasizes enrollment in clinical trials when available. Adjuvant systemic therapy outside a clinical trial is not recommended for primary resectable disease. For locally advanced unresectable, regional, and disseminated disease, ICIs are the preferred first-line approach. The following sections organize recommendations by stage and setting, with specific regimens and evidence.
Key Regimens
Treatment Response AssessmentClick to collapse
Title
Follow-up, Surveillance, and Response Assessment
Timing
Follow-up visits should begin immediately after treatment completion. Physical exam including complete skin and lymph node examination every 3β6 months for the first 3 years, then every 6β12 months thereafter. More frequent follow-up may be indicated for immunocompromised patients (MCC-6) [4,5].
Response Logic
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No standardized response criteria are specified for MCC; assessment is based on physical exam, imaging, and biomarkers. For patients on systemic therapy, standard RECIST 1.1 criteria are typically applied per clinical trial protocols.
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For patients receiving neoadjuvant nivolumab, response is assessed radiographically and pathologically. Adequate response allows proceeding to surgery; progression leads to discussion of local control vs. alternative systemic therapy (MCC-3).
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Serum MCPyV oncoprotein antibody testing: seronegative patients have higher recurrence risk. For seropositive patients, a rising titer may be an early indicator of recurrence. Baseline testing within 3 months of treatment; surveillance every 3 months (MCC-1, MCC-6) [14].
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ctDNA assessment: can detect disease burden in both virus-positive and virus-negative MCC. Typically becomes positive prior to or at time of clinically evident recurrence. Surveillance every 3 months (MCC-1, MCC-6) [15].
Imaging Recommendations
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Routine imaging surveillance is recommended for patients at high risk of recurrence: advancing age, immunosuppression, advancing stage (IIβIV), non-SLN metastases, MCPyV-negative status (MCC-6) [47].
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Surveillance imaging typically involves diagnostic CT of chest/abdomen/pelvis with oral and IV contrast; neck CT often included if primary lesion was on head/neck (MCC-6).
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Whole-body FDG-PET/CT may be indicated to evaluate for in-transit metastases if primary lesion is on extremity (MCC-6).
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Imaging should also be performed as clinically indicated for new symptoms (e.g., adenopathy, organomegaly, neurologic signs) (MCC-6).
Biopsy Or Salvage Logic
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If recurrence is suspected on physical exam or imaging, tissue biopsy (FNA, core, or excisional) with appropriate immunopanel is recommended to confirm diagnosis and rule out second primary (MCC-4, MCC-6).
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For local, locally advanced, or regional recurrence: treatment options include clinical trial (preferred), systemic therapy, RT, surgery, or best supportive care (MCC-6).
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For in-transit recurrence: manage per in-transit disease pathway (multidisciplinary consultation, clinical trial, surgery, RT, systemic therapy, local considerations) (MCC-6).
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For disseminated recurrence: treat as M1 disease (MCC-6).
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Under highly selective circumstances, resection of limited metastases can be considered after multidisciplinary consultation (MCC-5) [13].
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For patients who progress on anti-PD-(L)1 monotherapy, ipilimumab + nivolumab is particularly indicated as salvage therapy (MCC-D 3 of 4) [41,42].
SurveillanceClick to collapse
Clinical Follow Up Schedule
| Interval | Components |
|---|---|
| Every 3β6 months for the first 3 years | Physical exam including complete skin and complete lymph node examination [MCC-6] |
| Every 6β12 months thereafter | Physical exam including complete skin and complete lymph node examination [MCC-6] |
| More frequent for immunocompromised patients | Individualized based on risk [MCC-6, e] |
Imaging Strategy
- Routine surveillance imaging recommended for high-risk patients (stage β₯IIIB, immunosuppressed) [MCC-6, w].
- Modality: diagnostic CT of chest/abdomen/pelvis with oral and IV contrast; neck CT included if primary was on head/neck [MCC-6, v].
- Whole-body FDG-PET/CT may be indicated to evaluate for in-transit metastases if primary on extremity [MCC-6, v].
- Brain MRI with and without contrast if clinical suspicion of brain metastases or direct extension [MCC-2A, m].
- Imaging is also performed as clinically indicated for new symptoms or suspected recurrence [MCC-6].
Laboratory Monitoring
- MCPyV oncoprotein antibody testing: baseline within 3 months of treatment; surveillance every 3 months in seropositive patients; a rising titer may indicate recurrence [c, 55].
- ctDNA assessment: every 3 months for surveillance; can detect recurrence prior to clinical evidence; requires tissue-informed testing [d, 122].
- Other laboratory studies as clinically indicated (e.g., liver function tests if concern for metastases) [MCC-1, c].
Supportive Follow Up
- Patient education on self-examination of the skin and lymph nodes [MCC-6].
- Minimization of immunosuppression as clinically feasible in consultation with managing physician [MCC-1, e].
- Genetic counseling for patients diagnosed at age <50 years to evaluate for germline mutations in cancer-associated genes [MCC-1, f].
- Consider collecting additional tumor tissue from core biopsy for tissue-informed ctDNA testing prior to immunotherapy or RT [MCC-1].
- Referral to smoking cessation, nutrition, and physical activity programs as indicated.
ComplicationsClick to collapse
Disease-Related
| Complication | Management |
|---|---|
| Lymph node metastases | SLNB for staging; node dissection and/or RT for positive nodes; systemic therapy for unresectable disease [MCC-2, MCC-4]. |
| In-transit metastases | Biopsy confirmation; systemic therapy, surgery, RT; consider T-VEC or hyperthermic isolated limb infusion/perfusion [MCC-4]. |
| Distant metastases (lung, liver, bone, brain, distant skin/nodes) | Systemic therapy (immunotherapy preferred), RT for palliation, surgery for oligometastases in highly selected cases; best supportive care [MCC-5]. |
| Locoregional recurrence (local, regional, in-transit) | Treat per recurrence pathway: clinical trial, systemic therapy, RT, surgery; for in-transit recurrence follow N+ in-transit pathway [MCC-6, MCC-4]. |
| Second primary malignancies (SCC, BCC, melanoma, CLL, etc.) | Increased risk; routine skin surveillance and appropriate cancer screening [MS-5, 19,23,35,97-100]. |
Supportive CareClick to collapse
Best supportive care should be provided to all patients with MCC, following NCCN Guidelines for Palliative Care. For patients receiving immune checkpoint inhibitors, management of immune-related adverse events should follow NCCN Guidelines for Management of Immunotherapy-Related Toxicities [MCC-5, MCC-D 2]. The guideline emphasizes minimizing immunosuppression as clinically feasible, as immunosuppression is a risk factor for poor outcomes [MCC-1, e].
Not explicitly addressed in the MCC guideline; standard nutritional support per institutional practice.
Not explicitly addressed; for chemotherapy regimens (e.g., carboplatin/etoposide), standard antiemetic protocols per NCCN Antiemesis Guidelines are recommended.
Not explicitly addressed; use of G-CSF for febrile neutropenia prophylaxis should follow standard guidelines for chemotherapy regimens.
Not explicitly addressed; VTE prophylaxis per standard recommendations for hospitalized patients with cancer.
Not explicitly addressed; pain management per NCCN Adult Cancer Pain Guidelines may be needed for metastatic disease or post-surgical pain.
Not explicitly addressed; however, regular follow-up visits and patient education on self-examination are recommended. Anxiety and recurrence concerns should be addressed through multidisciplinary care.
Not explicitly addressed; general dental care before and during head/neck RT is recommended per standard practice.
PrognosisClick to collapse
Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine neoplasm with a high mortality rate, exceeding that of melanoma. The 5-year relative or MCC-specific survival rates range from 41% to 77%, depending on stage at presentation [2,10,13,18-23]. Approximately 63% of primary lesions grow rapidly within 3 months prior to diagnosis [7]. At least half of patients develop lymph node metastases, and nearly one third develop distant metastases [8-15]. Locoregional recurrence occurs in up to half of all cases [14-20].
By Stage
| Stage | Five Yr Survival | Context |
|---|---|---|
| Overall (all stages) | 41β77% | Range depending on stage at presentation; specific stage-level figures are not provided in the extracted guideline but referenced in multiple studies [2,10,13,18-23]. |
| Stage I/II (localized) | Not explicitly stated | Surgery Β± adjuvant RT is mainstay; risk factors for recurrence include LVI, immunosuppression, tumor >1 cm, positive margins, head/neck site, positive SLNB [MCC-2A]. |
| Stage III (regional) | Not explicitly stated | Nodal involvement carries worse prognosis; treatment includes node dissection, RT, and systemic therapy [MCC-4, MS-13]. |
| Stage IV (disseminated) | Not explicitly stated | Median OS ranges from 12.6 months (previously treated, avelumab) to 20.3 months (first-line avelumab) in clinical trials [285,287]. 5-year OS rate 26% (prior chemotherapy) and 38% (first-line) with avelumab [285,288]. |
Prognostic Factors
- Immunosuppression (solid organ transplant, CLL, HIV, chronic T-cell immunosuppression) is a major risk factor for poor outcomes and recurrence [19,38,40-46,49,114].
- Advancing stage of disease (stage IIβIV) [w].
- Primary tumor size >1 cm [k, 19,22,38,40-47,49,72,75-78,114,243].
- Lymphovascular invasion (LVI) [k, 22,72,75-78].
- Close or pathologically positive margins [k].
- Positive sentinel lymph node biopsy (SLNB) [k].
- Primary tumor site on head/neck [k].
- Non-SLN metastases [w].
- Merkel Cell polyomavirus (MCPyV) negative status [w] (associated with higher risk of recurrence [55,57-60]).
- Advanced age at diagnosis [w].
- Male sex (noted in some studies, but not uniformly confirmed) [w].
- Adverse histologic features: infiltrative growth pattern, high tumor depth, lack of brisk TILs, presence of second malignancy (e.g., concurrent SCC) [MS-4, MS-5, 76,80,83,86-91].
Follow UpClick to collapse
Post Curative Treatment
Close clinical follow-up is recommended starting immediately after diagnosis and treatment. Physical examination should include complete skin and complete lymph node examination every 3β6 months for the first 3 years, then every 6β12 months thereafter [MCC-6]. More frequent follow-up is indicated for immunocompromised patients [MCC-6, e]. Imaging and other studies should be performed as clinically indicated (e.g., for emergent adenopathy, organomegaly, new symptoms) [MCC-6]. For high-risk patients (stage IIIB or higher, immunosuppressed), routine imaging surveillance should be considered [MCC-6, v]. MCPyV oncoprotein antibody testing and ctDNA surveillance are often obtained every 3 months [c, d, 55, 122].
Surveillance Rationale
MCC can recur in up to half of patients, with 90% of recurrences occurring within 24 months (median time to recurrence ~8β9 months) [17,18,48,138, MS-21]. Early detection of recurrence may allow more effective salvage therapy. Risk factors for recurrence include immunosuppression, advancing age, stage IIβIV, non-SLN metastases, MCPyV-negative status, and other factors as determined by the treating physician [w]. Patients who are seronegative for MCPyV oncoprotein antibodies at diagnosis have higher recurrence risk and may benefit from more intensive surveillance [55]. ctDNA testing becomes positive prior to or at the time of clinically evident recurrence and should be considered for surveillance [122].
Late Effects Screening
- Second primary malignancies: Patients with MCC have increased risk of developing other skin cancers (SCC, BCC, melanoma), CLL, NHL, lung, breast, kidney cancers, and vice versa [19,23,35,97-100]. Lifelong routine skin surveillance is recommended.
- Radiation late effects: fibrosis, lymphedema (especially if groin irradiation), secondary radiation-induced malignancies (rare).
- Immunotherapy late effects: chronic endocrinopathies (thyroid, adrenal, pituitary insufficiency) may require long-term hormone replacement.
- Surgical late effects: lymphedema after SLNB or node dissection, particularly in groin; scar management.
Recurrence Patterns
Recurrence can be local (at primary site), regional (nodal basin), in-transit (between primary and nodal basin), or disseminated (distant metastases). Time to local recurrence is generally shorter than for regional recurrence; distant metastasis occurs later [16,17,19,225]. Detection of multiple distant metastases at once is not uncommon [125]. For local, locally advanced, or regional recurrence, options include clinical trial, systemic therapy, RT, and/or surgery [MCC-6]. In-transit recurrence follows the Clinical N+ in-transit pathway [MCC-6, MCC-4]. Disseminated recurrence is treated as M1 disease [MCC-6, MCC-5].
Key TrialsClick to collapse
| Acronym | Full Name | Year | N | Intervention | Comparator | Population | Primary Endpoint | Key Result | Secondary Outcomes | Practice Change | Journal |
|---|---|---|---|---|---|---|---|---|---|---|---|
| JAVELIN Merkel 200 Part A | Avelumab in Patients with Chemotherapy-Refractory Metastatic Merkel Cell Carcinoma | 2016 | 88 | Avelumab 10 mg/kg IV every 2 weeks | None (single-arm) | Patients with stage IV distant MCC progressing after β₯1 prior chemotherapy | Objective response rate (ORR) by independent review | ORR 33% (95% CI, 23.3β43.8); median OS 12.6 months (95% CI, 7.5β17.1); 5-year OS rate 26% (95% CI, 17β36) [282,285] | Median PFS not reported; durable responses; biomarker analyses [286] | Established avelumab as effective therapy for chemotherapy-refractory metastatic MCC; led to FDA approval. | Lancet Oncology |
| JAVELIN Merkel 200 Part B | First-Line Avelumab in Metastatic Merkel Cell Carcinoma | 2018 | 116 | Avelumab 10 mg/kg IV every 2 weeks | None (single-arm) | First-line treatment for stage IV metastatic MCC | ORR by independent review | ORR 39.7% (95% CI, 30.7β49.2); median PFS 4.1 months (95% CI, 1.4β6.1); median OS 20.3 months (95% CI, 12.4βNE); 4-year OS rate 38% (95% CI, 29β47) [287,288] | PD-L1 positive tumor median OS 38.7 months vs 16.1 months for PD-L1 negative [288] | First-line immunotherapy for metastatic MCC; increased use of avelumab as standard. | JAMA Oncology |
| Nghiem et al. (Pembrolizumab Phase II) | Pembrolizumab for Advanced Merkel Cell Carcinoma (KEYNOTE-017) | 2019 | 50 | Pembrolizumab 2 mg/kg IV every 3 weeks for up to 2 years | None (single-arm) | Patients with distant metastatic or locoregional MCC not amenable to definitive surgery/RT, no prior systemic therapy | ORR by RECIST v1.1 | ORR 58% (95% CI, 43.2β71.8); complete response 30%; median PFS 16.8 months (95% CI, 4.6β43.4); 3-year OS 59.4% (89.5% for responders) [296,297] | Median OS not reached; durable responses; safety profile consistent with pembrolizumab | Pembrolizumab is a preferred first-line therapy for advanced MCC; supported FDA approval. | Journal of Clinical Oncology |
| CheckMate 358 | Neoadjuvant Nivolumab for Resectable Merkel Cell Carcinoma | 2020 | 39 | Neoadjuvant nivolumab 240 mg IV every 2 weeks for up to 4 doses before surgery | None (single-arm) | Resectable MCC stage IIAβIV (M1 with resectable disease) with β₯1 dose of neoadjuvant nivolumab | Pathologic complete response (pCR) | pCR in 47.2% (17/36) of patients who underwent surgery; radiographic tumor reduction β₯30% in 54.5% of evaluable patients [293] | Median recurrence-free survival and overall survival not reached at median follow-up 20.3 months | Neoadjuvant nivolumab is included as a useful option in certain circumstances for locally advanced MCC where curative surgery and RT are not feasible [MCC-3]. | Journal of Clinical Oncology |
| POD1UM-201 | Retifanlimab in Patients with Advanced or Metastatic Merkel Cell Carcinoma | 2021 | 87 (chemotherapy-naΓ―ve group evaluated) | Retifanlimab-dlwr 500 mg IV every 4 weeks | None (single-arm) | Unresectable locally advanced or metastatic MCC, no prior anti-PD-1/L1 therapy | ORR by independent review | ORR 46.2% (30/65); complete response 12.3%; disease control rate 53.8% [298] | Not reported in abstract | Retifanlimab-dlwr is listed as a preferred regimen for many disease states in the guideline, indicating its emerging role. | Journal for ImmunoTherapy of Cancer (abstract) |
| Kim et al. (Ipilimumab + Nivolumab Β± SBRT) | Combined Nivolumab and Ipilimumab with or without Stereotactic Body Radiation Therapy for Advanced Merkel Cell Carcinoma: A Randomised, Open Label, Phase 2 Trial | 2022 | 50 | Nivolumab + ipilimumab Β± SBRT (cohort A with SBRT, cohort B without) | Two cohorts (non-randomized comparison of SBRT addition) | Advanced MCC, including both ICI-naΓ―ve and prior ICI-exposed patients | ORR by RECIST 1.1 | ORR 100% (22/22) in ICI-naΓ―ve (9 complete responses, 41%); ORR 31% (8/26) in prior ICI; no significant difference in ORR with SBRT (P=0.26) [22] | Grade 3/4 TRAEs: 40% cohort A, 32% cohort B; median follow-up 14.6 months | Ipilimumab + Nivolumab is recommended as other recommended regimen for regional/disseminated disease and particularly indicated for PD-1 refractory disease [MCC-D 3,4]. | Lancet |
Clinical PearlsClick to collapse
- Pearl 1: SLNB is the most reliable staging tool for subclinical nodal disease; it should be performed prior to or at the time of definitive tumor excision, especially in head/neck cases where drainage patterns can be complex [MCC-2, MCC-C, 246].
- Pearl 2: For patients with β₯1 adverse risk factors (LVI, immunosuppression, tumor >1 cm, positive margins, positive SLNB, head/neck site), adjuvant RT to the primary tumor site should be strongly considered. Delay >7β8 weeks from surgery to RT initiation is associated with worse outcomes [MCC-2A, k; MCC-B 1, 240].
- Pearl 3: Narrow surgical margins (clear or microscopically positive) are acceptable if adjuvant RT is planned; this approach balances morbidity and avoids delay to RT [MCC-2, l; 179].
- Pearl 4: Immunotherapy (PD-1/PD-L1 inhibitors) is the preferred systemic therapy for advanced MCC over chemotherapy, due to improved durability of response and more favorable safety profile. Chemotherapy should be reserved for patients who are not candidates for immunotherapy or have progressed on it [MCC-D, MS-20].
- Pearl 5: MCPyV oncoprotein antibody testing and ctDNA monitoring every 3 months can aid in early detection of recurrence. A rising antibody titer in initially seropositive patients or conversion of ctDNA from negative to positive should prompt imaging investigation [c, d, 55, 122].
- Pearl 6: Multidisciplinary consultation at a center with specialized expertise is recommended for all patients with MCC, particularly those with locally advanced, regional, or disseminated disease, to coordinate optimal sequencing of surgery, RT, and systemic therapy [MCC-1, MCC-3, MCC-4, MCC-5].
- Pearl 7: For patients with locally advanced MCC who are surgical candidates, neoadjuvant nivolumab can achieve high rates of pathologic complete response (47.2% in CheckMate 358) and may enable R0 resection. Close monitoring for progression is required [MCC-3, 293].
- Pearl 8: Immunosuppressed patients have worse outcomes and higher recurrence risk; immunosuppression should be minimized when feasible, and patients may require more frequent follow-up. Consider empiric nodal RT if profound immunosuppression compromises SLNB reliability [MCC-1, e; MCC-2A, p].