Thymic Cancer
Thymoma and thymic carcinoma — surgery, RT, systemic therapy
DefinitionClick to collapse
Thymoma and thymic carcinoma are rare neoplasms originating in the epithelial cells of the thymus gland, located in the anterior mediastinum. The thymus is a lymphoid organ situated anterior to the heart and great vessels, bordered posteriorly by the pericardium, inferiorly by the diaphragm, and laterally by the pleural sacs. Thymomas are characterized by their relatively indolent growth pattern and propensity for local invasion, though they rarely metastasize. They are the most common primary tumors of the anterior mediastinum, occurring in approximately two per million per year in the United States [3,4]. Thymic carcinomas are less common, with an estimated annual incidence of 0.48 per million in the United States [4]. These tumors are more aggressive, with frequent presentation as advanced or metastatic disease, and a markedly different histological and clinical course compared to thymomas [5-8]. A well-defined anterior mediastinal mass in the thymic bed, with negative tumor markers (AFP, beta-hCG), absence of other adenopathy, and lack of continuity with the thyroid, is highly suggestive of a thymic tumor [2]. Differentiation from other mediastinal pathologies (e.g., lymphomas, germ cell tumors, thymic cysts) is critical for management [16-22].
EpidemiologyClick to collapse
SubtypesClick to collapse
Thymoma - Type A
A thymic epithelial tumor composed of bland spindle or oval epithelial cells, rarely polygonal, with a fascicular, storiform, or pericytomatous growth pattern. Most cases lack necrosis, have a low mitotic count, and a low Ki-67 index. Atypical type A thymomas may have higher mitotic counts and focal necrosis.
Thymoma - Type AB
A thymic tumor with a lobulated growth pattern, comprising an admixed spindle cell-predominant lymphocyte-poor component (type A) and a lymphocyte-rich component (type B). It contains bland spindle, oval, and focally polygonal thymic epithelial cells and focal or diffuse abundance of immature T cells.
Thymoma - Type B1
A thymic epithelial tumor with organoid (corticomedullary) architecture showing cortical predominance. It features dispersed, non-clustered thymic epithelial cells among densely packed lymphocytes, with obligatory medullary islands.
Thymoma - Type B2
A tumor with a lobulated architecture, abundance of lymphocytes, and polygonal/oval neoplastic epithelial cells that are more numerous than in the normal thymic cortex and often present in clusters.
Thymoma - Type B3
A lobulated tumor consisting of sheets of mildly/moderately atypical, polygonal tumor cells, interspersed perivascular spaces, and a paucity of lymphocytes.
Thymoma - Micronodular Thymoma with Lymphoid Stroma
Characterized by multiple small discrete nodules composed of bland spindle or oval epithelial cells, within an abundant epithelial cell-free lymphoid stroma.
Thymoma - Metaplastic Thymoma
A biphasic thymic tumor with anastomosing islands of polygonal epithelial cells, which may show variable nuclear atypia, against a background of bland-looking spindly cells.
Thymoma - Lipofibroadenoma
A benign thymic tumor resembling fibroadenoma of the breast, with a predominance of fibrous tissue over adipocytes and delicate strands of epithelial cells.
Thymic Carcinoma - Squamous Cell Carcinoma, NOS
An invasive squamous cell carcinoma of the thymus, often accompanied by desmoplastic to sclerohyaline stroma. It requires exclusion of invasion from adjacent pulmonary carcinoma or metastasis.
Thymic Carcinoma - Basaloid Carcinoma
A basaloid carcinoma of the thymus with nests or cystic spaces lined by basaloid neoplastic cells with peripheral palisading.
Thymic Carcinoma - Lymphoepithelial Carcinoma
A primary thymic carcinoma featuring sheets, nests, and cords of carcinoma cells with a syncytial appearance, vesicular chromatin, and prominent nucleoli, with many admixed lymphocytes and plasma cells.
Thymic Carcinoma - Adenocarcinoma, NOS
Adenocarcinoma of the thymus after exclusion of mediastinal metastasis from other sites and defined types of thymic adenocarcinoma.
Thymic Carcinoma - Low-grade Papillary Adenocarcinoma
A primary thymic low-grade adenocarcinoma with tubulopapillary growth, lined by cuboidal or polygonal cells.
Thymic Carcinoma - Thymic Carcinoma with Adenoid Cystic Carcinoma-like Features
Thymic carcinoma morphologically similar to adenoid cystic carcinoma, but generally lacking true glands within the cribriform-basaloid islands. Requires exclusion of metastasis from salivary gland, lung, or breast.
Thymic Carcinoma - Adenocarcinoma, Enteric-type
A primary thymic tumor mimicking colorectal adenocarcinoma. Requires exclusion of metastasis from an enteric primary.
Thymic Carcinoma - Adenosquamous Carcinoma
A primary thymic carcinoma with both squamous and glandular differentiation, in which each component constitutes ≥10% of the tumor within a resection specimen. Requires exclusion of mucoepidermoid carcinoma.
Thymic Carcinoma - NUT Carcinoma
Demonstration of NUTM1 rearrangement by molecular methods or NUT-positive IHC in a poorly differentiated squamous cell carcinoma or other poorly differentiated carcinoma.
Thymic Carcinoma - Mucoepidermoid Carcinoma
A primary thymic carcinoma characterized by a combination of mucus-producing, intermediate, and squamoid cells growing in nests and cystic structures. In high-grade MEC, the diagnosis requires the presence of at least focal intracellular mucin.
Thymic Carcinoma - Clear Cell Carcinoma
Islands and trabeculae of carcinoma cells with clear cytoplasm. Abundant hyalinized stroma in hyalinizing clear cell carcinoma.
Thymic Carcinoma, NOS
Exclusion of any of the above thymic carcinoma types. Currently comprises hepatoid carcinoma, rhabdoid carcinoma, undifferentiated large cell carcinoma with Castleman disease-like reaction, and sebaceous carcinoma.
Thymic Neuroendocrine Neoplasms - Typical Carcinoid
A primary thymic neuroendocrine tumor (NET) with low-grade nuclear features, neuroendocrine morphology (e.g., trabecular or rosetting), absence of necrosis, and mitotic count of <2 mitoses/2 mm².
Thymic Neuroendocrine Neoplasms - Atypical Carcinoid
Same as Typical Carcinoid, but with comedonecrosis and/or mitotic count of 2–10 mitoses/2 mm².
Thymic Neuroendocrine Neoplasms - Small Cell Carcinoma
Radiological evidence of thymic origin. Requires exclusion of a tumor spreading from the lung or metastatic from another extrapulmonary site to the thymus. A tumor consisting purely of small cells with characteristic morphology similar to lung SmCCs. Combined SmCC is a small carcinoma combined with another histology such as thymoma or other type of thymic carcinoma.
Thymic Neuroendocrine Neoplasms - Large Cell Neuroendocrine Carcinoma
Neuroendocrine morphology, mitotic count of >10 mitoses/2 mm², necrosis (often geographical), and positive neuroendocrine IHC.
Molecular PathogenesisClick to collapse
The provided text does not contain specific information regarding key genomic events, driver mutations, signaling pathways, or chromosomal abnormalities with associated frequencies for thymomas or thymic carcinomas. The discussion focuses on clinical management, histologic classification, and treatment outcomes. Therefore, a detailed molecular pathogenesis section cannot be derived from this source material.
Risk FactorsClick to collapse
Unknown etiology for thymoma
The etiology of thymomas is unknown. Alcohol, tobacco smoking, and ionizing radiation do not appear to be risk factors for thymomas.
Race/Ethnicity (for thymoma)
The incidence of thymomas is reported to be higher among Black and Asian individuals.
Clinical FeaturesClick to collapse
Typical Presentation
Thymomas and thymic carcinomas are rare epithelial tumors originating in the thymus, with thymomas being the most common primary anterior mediastinal tumors [1,2]. Thymomas typically occur in adults and are rare in children and adolescents [3,22,121]. The etiology is unknown, with alcohol, tobacco smoking, and ionizing radiation not appearing to be risk factors [3]. There is a reported higher incidence among certain racial and ethnic subgroups, specifically Black and Asian individuals [3,122]. Patients may be asymptomatic or present with symptoms such as chest pain, cough, or dyspnea. Although thymomas can be locally invasive (e.g., to pleura, lung), they uncommonly spread to regional lymph nodes or extrathoracic sites [7,123-125]. A key characteristic is the association with autoimmune paraneoplastic syndromes, most notably myasthenia gravis, which occurs in approximately one-third of patients [126,129,130]. Hypogammaglobulinemia and pure red cell aplasia are other associated syndromes, occurring in <10% of patients [126-128,130]. Mortality is often not directly related to the thymoma itself [40].
Symptoms
Chest pain
A common presenting symptom.
Cough
A common presenting symptom.
Dyspnea
A common presenting symptom, can be due to mass effect or associated myasthenia gravis.
Symptoms of myasthenia gravis
Includes ptosis, diplopia, drooling, proximal muscle weakness, hoarseness, and/or dyspnea. Occurs in ~1/3 of thymoma patients [126,129,130].
Superior vena cava syndrome
More characteristic of thymic carcinoma.
Symptoms from pericardial/pleural effusion
Thymic carcinomas often cause these effusions.
Signs
Mediastinal mass on imaging
Well-defined round or oval mass in the thymic bed on CT, often without lymph node enlargement [33-35].
Neurological signs of myasthenia gravis
Proximal muscle weakness, ptosis, diplopia.
Red FlagsClick to collapse
New-onset or worsening symptoms of myasthenia gravis (ptosis, diplopia, proximal weakness, dyspnea) [131-133].
Superior vena cava syndrome (facial/arm swelling, plethora, dyspnea when leaning forward).
Evidence of invasion into adjacent structures on imaging (e.g., great vessels, lung, pericardium).
Pleural or pericardial effusions causing respiratory compromise.
Symptoms suggestive of extrathoracic metastases (e.g., bone pain, neurological deficits).
InvestigationsClick to collapse
Diagnostic
Chest CT with contrast
Essential initial evaluation for a mediastinal mass to characterize location, size, and features suggestive of thymic malignancy [30-32,34]. A well-defined mass in the thymic bed, negative tumor markers, no other adenopathy, and no continuity with thyroid suggests a thymic tumor [2].
Chest MRI (with and without contrast)
Can better discriminate thymic malignancy from thymic cyst or hyperplasia compared to CT, potentially avoiding unnecessary thymectomy. Also appropriate if patients cannot tolerate iodinated contrast [35,36].
Core needle biopsy
Recommended for locally advanced or metastatic disease to obtain tissue diagnosis [THYM-2].
Open biopsy
May be considered if core biopsy is not feasible or not diagnostic. A transpleural approach should be avoided due to risk of seeding [THYM-2, 132,138].
Staging
Chest CT with contrast
Primary imaging for local staging and assessing resectability [THYM-1, THYM-4].
FDG-PET/CT scan (skull base to mid-thigh)
As clinically indicated, for comprehensive staging to evaluate extent of disease, including nodal and distant metastases [THYM-1, THYM-4].
Chest MRI
Appropriate alternative to CT in certain clinical situations, e.g., for better soft tissue detail or if contrast allergy exists [THYM-3, THYM-4, footnote m].
Brain imaging (MRI preferred)
Consider in thymic carcinoma, which can metastasize to brain [Discussion].
Biomarkers
Serum beta-hCG and AFP
To rule out germ cell tumors, which can also present as anterior mediastinal masses [THYM-1, 37].
Octreotide scan or dotatate PET/CT
To assess for somatostatin receptor expression, which informs use of octreotide therapy in thymoma [THYM-C 2 of 3, 13,14]. Dotatate PET/CT is preferred if available.
Immunohistochemistry (IHC)
Essential for subtyping thymic epithelial tumors per WHO classification (e.g., cytokeratins, p40/p63, TdT, CD5, KIT, CD117) [THYM-D, 1,2].
Molecular testing (e.g., NGS, FISH for NUTM1)
Consider for certain subtypes (e.g., NUT carcinoma requires demonstration of NUTM1 rearrangement) or to identify potential therapeutic targets (e.g., KIT mutation) [THYM-D, 1,2].
StagingClick to collapse
Both the Masaoka-Koga staging system and the AJCC 8th/9th edition TNM system are provided. Treatment recommendations in the NCCN Guidelines primarily refer to Masaoka-Koga staging, as much clinical evidence was generated using this system [Discussion]. The AJCC 9th edition TNM definitions are provided in Table 2 and the prognostic groups in Table 3 [ST-2, ST-3].
T Categories
| Stage | Description |
|---|---|
| TX | Primary tumor cannot be assessed. |
| T0 | No evidence of primary tumor. |
| T1 | Tumor limited to the thymus with or without encapsulation, or directly invades into the mediastinal fat only, or directly invades the mediastinal pleura but does not involve any other mediastinal structure. |
| T1a | Tumor ≤5 cm in greatest dimension with characteristics of T1. |
| T1b | Tumor >5 cm in greatest dimension with characteristics of T1. |
| T2 | Tumor with direct invasion of the pericardium (either partial or full thickness), or the lung, or the phrenic nerve. |
| T3 | Tumor with direct invasion into any of the following: brachiocephalic vein, superior vena cava, chest wall, or extrapericardial pulmonary arteries or veins. |
| T4 | Tumor with direct invasion into any of the following: aorta (ascending, arch, or descending), arch vessels, intrapericardial pulmonary artery or veins, myocardium, trachea, esophagus. |
N Categories
| Stage | Description |
|---|---|
| NX | Regional lymph nodes cannot be assessed. |
| N0 | No tumor involvement of regional lymph node(s). |
| N1 | Tumor involvement of anterior (perithymic) lymph nodes. |
| N2 | Tumor involvement of deep intrathoracic or cervical lymph nodes (e.g., paratracheal, subcarinal, aortopulmonary window, hilar, jugular, and/or supraclavicular node). |
M Categories
| Stage | Description |
|---|---|
| cM0 | No distant metastasis. |
| cM1 | Distant metastasis. |
| cM1a | Separate pleural or pericardial nodule(s). |
| cM1b | Pulmonary intraparenchymal nodule or other distant metastasis. |
| pM1 | Microscopic confirmation of distant metastasis. |
| pM1a | Microscopic confirmation of separate pleural or pericardial nodule(s). |
| pM1b | Microscopic confirmation of pulmonary intraparenchymal nodule or other distant metastasis. |
Stage Groupings
| Group | Criteria | Clinical Meaning | Five Yr Survival | Treatment Intent |
|---|---|---|---|---|
| Stage I | T1a,b, N0, M0 | Early-stage disease, excellent prognosis with surgery alone. | Approximately 90% for thymoma [137]; 5-year survival for thymic carcinoma with R0 resection is ~60-70% [9,10]. | Curative. |
| Stage II | T2, N0, M0 | Local invasion of pericardium, lung, or phrenic nerve. | 70% for thymoma [137]. | Curative. |
| Stage IIIA | T3, N0, M0 | Invasion into major vessels (brachiocephalic vein, SVC), chest wall, or extrapericardial pulmonary vessels. | 55% for thymoma [137]. | Curative. |
| Stage IIIB | T4, N0, M0 | Invasion into aorta, arch vessels, intrapericardial pulmonary vessels, heart, trachea, or esophagus. | Poor prognosis. | Curative. |
| Stage IVA | Any T, N1, M0 OR Any T, N0-N1, M1a | Involvement of anterior lymph nodes (N1) OR pleural/pericardial dissemination (M1a). | 35% for thymoma [137]. | Often palliative, but multimodal therapy with curative intent may be attempted in selected cases. |
| Stage IVB | Any T, N2, M0-M1a OR Any T, Any N, M1b | Involvement of deep intrathoracic/cervical nodes (N2) OR distant metastasis (M1b). | Poor prognosis. | Palliative. |
Staging Pearls
- The Masaoka-Koga system is more commonly used in clinical practice and for treatment decisions in these guidelines [Discussion].
- Resectability, defined as complete (R0) resection, is a critical prognostic factor and should be determined by a thoracic surgeon in a multidisciplinary context [THYM-2, e].
- For thymoma, late recurrences (≥10 years) can occur due to indolent growth, necessitating long-term surveillance [Discussion].
- Thymic carcinomas are often diagnosed at advanced stages (III or IV) and have a higher risk of recurrence compared to thymomas [9,10, Discussion].
- The AJCC 9th edition TNM system provides more granular T staging (T1a vs T1b) and formalizes nodal staging (N1, N2), which can be useful for prognostication [ST-2, ST-3].
- Pleural or pericardial nodules are classified as M1a (Stage IVA), while parenchymal pulmonary nodules or other distant metastases are M1b (Stage IVB) [ST-2].
Management PrinciplesClick to collapse
Thymomas and thymic carcinomas are rare thymic epithelial tumors. Management is complex and requires a multimodal approach involving surgery, radiation therapy (RT), and/or systemic therapy, depending on the disease stage and completeness of resection. A complete (R0) surgical resection is a critical prognostic factor and the primary oncologic goal for resectable tumors [5,7,12,52-60]. Treatment philosophy emphasizes individualization based on disease extent, histologic subtype (WHO classification), and resectability, which is defined as the potential for an R0 resection. All patients should be evaluated and managed by a multidisciplinary team with experience in these tumors [5,7,13,22,134].
Curative
Patients with surgically resectable disease (Masaoka-Koga stage I–III) or localized advanced disease amenable to multimodal therapy.
The primary treatment is surgical resection (total thymectomy and excision of contiguous disease). For stage I with no capsular invasion (R0), observation is recommended postoperatively. For higher stages (II–IV) or with capsular invasion, postoperative RT is recommended even after R0 resection. For R1 or R2 resections, postoperative RT with or without chemotherapy is recommended. For locally advanced, potentially resectable disease (uncertain R0 resection), neoadjuvant systemic therapy should be considered to improve resectability before surgery [5,7,12,22,61-64,135,136].
Palliative/Non-Curative
Patients with unresectable advanced, metastatic, or recurrent disease.
Treatment is directed at symptom control, disease stabilization, and prolonging survival. Options include definitive RT (conventional fractionation or SABR for limited lesions), concurrent chemoradiation, systemic therapy, or observation, depending on disease dissemination and patient fitness. Local therapies like image-guided thermal ablation may be considered for select metastatic or recurrent lesions. The natural history can be indolent, even for metastatic thymoma, allowing for durable local control with RT [5,13,56,98,100,114-117,153-155].
All patients with a likely thymic tumor should be treated by a multidisciplinary team (MDT) with experience in the management of thymomas and thymic carcinomas. The team should include radiation oncologists, thoracic surgeons, medical oncologists, neurologists (especially for patients with myasthenia gravis), pathologists, and diagnostic imaging specialists [5,7,13,22,134]. Determination of resectability must be made by a thoracic surgeon, preferably with a primary focus on thoracic oncology, and in multidisciplinary consultation as needed [e].
The guidelines do not specify explicit performance status (PS) thresholds for treatment eligibility. However, the decision for surgery, definitive RT, or systemic therapy is inherently based on a patient's overall medical fitness and ability to tolerate the proposed treatment. Patients must be medically controlled prior to surgical resection, especially for paraneoplastic syndromes like myasthenia gravis. The MDT discussion integrates PS and comorbidities to determine the most appropriate, individualized treatment plan [a, THYM-2].
Management PathwaysClick to collapse
Branching: Masaoka-Koga stage, Capsular invasion status, Completeness of resection (R0/R1/R2)
Branching: Resectability of primary and metastatic sites, Disease dissemination (localized vs. extrathoracic), Patient fitness
Branching: Masaoka-Koga stage, Completeness of resection (R0/R1/R2)
Branching: Resectability, Disease dissemination, Patient fitness
Pretreatment EvaluationClick to collapse
Initial Diagnostic Workup for Mediastinal Mass
Pathological Diagnosis
Preoperative Assessment
Staging
SurgeryClick to collapse
Surgery is the primary and potentially curative treatment modality for resectable thymomas and thymic carcinomas. Complete (R0) resection is a critical prognostic factor [5,7,12,52-60].
Should be performed by thoracic surgeons with experience in managing thymomas and thymic carcinomas [THYM-A].
Locally advanced and resectable stage ≥ II cases should be discussed by an MDT [THYM-A].
Surgical biopsy should be avoided if resectable thymoma is strongly suspected to prevent tumor seeding [THYM-A].
Biopsy of a possible thymoma should avoid a transpleural approach to prevent converting stage I to stage IV [a, THYM-A].
Goal is complete excision of the lesion with total thymectomy and complete resection of contiguous and noncontiguous disease [THYM-2, THYM-A].
Complete resection may require resection of adjacent structures (pericardium, phrenic nerve, pleura, lung, major vascular structures). Bilateral phrenic nerve resection should be avoided due to severe respiratory morbidity [THYM-A].
Surgical clips should be placed at areas of close margins, residual disease, or tumor adhesion to guide RT [THYM-A].
During thymectomy, pleural surfaces should be examined for metastases. Resection of pleural metastases to achieve complete gross resection is appropriate if feasible [THYM-A].
Minimally invasive procedures (VATS, RATS) for thymectomy may be considered if all oncologic principles of open thymectomy are met and performed in specialized centers by experienced surgeons [1-15, THYM-A].
Debulking tumors is discouraged [65,66, THYM-A].
Procedures
Total Thymectomy (Open or Minimally Invasive)
Standard of care for resectable thymomas and thymic carcinomas [THYM-2].
Radiation TherapyClick to collapse
RT is used in multiple settings: as definitive therapy for unresectable disease, as adjuvant therapy after surgery (especially for incomplete resection or higher-stage disease), and as local therapy for recurrent or metastatic lesions [90].
Principles
- Recommendations should be made by radiation oncologists with experience in managing thymomas and thymic carcinomas [THYM-B].
- Definitive RT for unresectable disease, incompletely resected invasive thymoma or thymic carcinoma, or as adjuvant therapy after systemic therapy and surgery [THYM-B].
- Close communication between radiation oncologist and surgeon regarding operative findings is essential to define the target volume at risk [THYM-B].
- Communication with pathologist regarding histology, disease extent, and surgical margins is important [THYM-B].
- Review of preoperative imaging and co-registration into the planning system are helpful [THYM-B].
- Extensive elective nodal irradiation (ENI) is not recommended because thymomas do not commonly metastasize to regional lymph nodes [7, THYM-B].
Dose Frameworks
| Name | Total Dose | Dose Per Fraction | Fractions | Schedule | Indication |
|---|---|---|---|---|---|
| Adjuvant RT, clear/close margins | 45–50 Gy | 1.8–2.0 Gy | 25–28 | Conventional fractionation | Postoperative adjuvant treatment for clear or close surgical margins [THYM-B]. |
| Adjuvant RT, microscopically positive margins (R1) | 54 Gy | 1.8–2.0 Gy | 30 | Conventional fractionation | Postoperative adjuvant treatment for microscopically positive (R1) resection margins [THYM-B]. |
| Definitive RT for unresectable disease or gross residual disease (R2) | 60–66 Gy | 1.8–2.0 Gy | 33–37 | Conventional fractionation | For patients with unresectable disease or gross residual disease (R2) after surgery [3, THYM-B]. |
| Palliative RT | Various (e.g., 8 Gy in 1 fx, 20 Gy in 5 fx, 30 Gy in 10 fx up to definitive doses) | Varies | Varies | Based on treatment objectives | Palliative setting; given the long natural history, even definitive doses may be considered for durable local control [THYM-B]. |
Approaches
| Name | Dose Fractionation | Concurrent Chemotherapy | Indication | Key Trial | Toxicities |
|---|---|---|---|---|---|
| 3D Conformal Radiation Therapy (3D-CRT) | As per dose frameworks | As per clinical setting (e.g., cisplatin/etoposide, carboplatin/paclitaxel) | Minimum technological standard for RT [THYM-B]. | Not specified. | Standard RT toxicities; conservative heart dose limits recommended [THYM-B]. |
| Intensity-Modulated Radiation Therapy (IMRT) / Volumetric Modulated Arc Therapy (VMAT) | As per dose frameworks | As per clinical setting | Preferred over 3D-CRT to improve target coverage and dose conformity and further reduce cardiac dose [THYM-B]. | Not specified. | May reduce cardiac dose compared to 3D-CRT. |
| Proton Therapy | As per dose frameworks | As per clinical setting | Appropriate and shown to improve dosimetry, allowing for better sparing of normal organs (lungs, heart) with favorable local control and toxicity [8,9, THYM-B]. | Not specified. | Favorable normal organ sparing (lungs, heart) [8,9]. |
| Stereotactic Ablative Radiotherapy (SABR/SBRT) | High dose per fraction (e.g., 50 Gy in 5 fractions) | Not typically concurrent | May be appropriate for limited focal metastases [114,115, THYM-B]. | Not specified. | High local control rates with acceptable toxicity for small metastases. |
Systemic TherapyClick to collapse
Systemic therapy is used in multiple settings: neoadjuvant for potentially resectable advanced disease, definitive for unresectable advanced/metastatic disease, and adjuvant for incompletely resected disease. Treatment regimens differ for thymoma and thymic carcinoma. Thymomas are considered chemosensitive, while thymic carcinomas are generally less chemosensitive. PD-1/PD-L1 inhibitor therapy is not recommended for thymoma and is associated with high rates of immune-related adverse events in thymic carcinoma [d, e, 180-182, 201, THYM-C].
Key Regimens
Treatment Response AssessmentClick to collapse
Title
Post-Treatment Evaluation and Surveillance
Timing
Surveillance imaging should be performed routinely after completion of primary treatment.
Response Logic
Imaging response is assessed using CT with contrast. For thymoma, the ITMIG has proposed radiographic assessment using modified RECIST criteria [123], but the guidelines do not mandate a specific response assessment method.
Biopsy Or Salvage Logic
The duration for surveillance has not been established [n]. Patients with thymoma have an increased risk for second malignancies, although no particular screening studies are recommended. Recurrent disease should be managed by the MDT, with treatment options similar to those for newly diagnosed disease (see Management Pathways) [THYM-3, THYM-4]. Late recurrences (≥10 years) are documented for thymoma [56].
SurveillanceClick to collapse
Clinical Follow Up Schedule
- Thymoma, stage I (R0, no capsular invasion): Chest CT with contrast every 6-12 months for 2 years, then annually until year 10 [THYM-3]
- All other thymoma patients: Chest CT with contrast every 6 months for 2 years, then annually until year 10 [THYM-3]
- Thymic carcinoma, stage I (R0, no capsular invasion): Chest CT with contrast every 6-12 months for 2 years, then annually until year 5 [THYM-3]
- All other thymic carcinoma patients: Chest CT with contrast every 3-6 months for 2 years, then annually until year 5 [THYM-3]
Imaging Strategy
- Chest CT with contrast is the primary imaging modality for surveillance [THYM-3]
- MRI is an appropriate alternative to CT in certain clinical situations, including if patients cannot tolerate contrast or to decrease radiation in young patients who will be screened for many years [35, footnote m]
- FDG-PET/CT (skull base to mid-thigh) as clinically indicated for initial evaluation [THYM-1]
- FDG-PET/CT includes skull-base to mid-thigh [footnote p, THYM-4]
- Chest MRI with and without contrast as clinically indicated [THYM-1]
- Detection of thymic malignancy versus thymic cyst or thymic hyperplasia can be better discriminated with chest MRI compared to chest CT [36]
Laboratory Monitoring
- Serum beta-hCG, AFP as appropriate (to rule out germ cell tumors) [THYM-1]
- CBC, platelets as part of initial evaluation [THYM-1]
- DPYD testing before fluoropyrimidine therapy per NCCN Colon Cancer Guidelines [179, footnote g]
Supportive Follow Up
- Clinical evaluation for signs of myasthenia gravis and other paraneoplastic syndromes [THYM-1, THYM-3]
- Pulmonary function tests as clinically indicated [THYM-1]
- Distress assessment using NCCN Distress Thermometer and Problem List [THYM-1, footnote c]
- Assessment for treatment-related adverse events based on therapies received
- Duration, frequency, and type of imaging for surveillance have not been prospectively evaluated [footnote n]
ComplicationsClick to collapse
Disease-Related
| Complication | Management |
|---|---|
| Myasthenia gravis | Approximately one-third of patients with thymomas may have myasthenia gravis, the most common paraneoplastic syndrome associated with thymoma [126,129,130]. Patients should be evaluated clinically for signs of myasthenia gravis before surgical resection [131-133]. If patients have myasthenia gravis, they should receive treatment by a neurologist with experience in myasthenia gravis prior to surgical resection. Symptoms include ptosis, diplopia, drooling, proximal muscle weakness, hoarseness, and/or dyspnea [126-128]. |
| Hypogammaglobulinemia | Associated with thymoma; should be evaluated as part of paraneoplastic workup [126-128]. The clinical spectrum includes Good syndrome (thymoma-associated immunodeficiency) and beyond [127]. |
| Pure red cell aplasia | Associated with thymoma; estimated to occur in <10% of patients with thymoma [130]. Requires appropriate hematologic workup and management. |
| Other paraneoplastic syndromes | Other paraneoplastic syndromes have been estimated to occur in <10% of patients with thymoma [130]. All patients with thymoma should be evaluated clinically for signs of autoimmune paraneoplastic disorders [THYM-1]. |
| Pericardial and pleural effusions | Thymic carcinomas often cause pericardial and pleural effusions [9,10]. May require drainage procedures and management as clinically indicated. |
| Superior vena cava syndrome | Symptom that patients with thymic carcinoma may experience related to mass effect [11]. Requires urgent management and may indicate advanced disease. |
| Local invasion | Thymomas can be locally invasive to pleura and lung but uncommonly spread to regional lymph nodes or extrathoracic sites [7,123-125]. Complete resection may require resection of adjacent structures including pericardium, phrenic nerve, pleura, lung, and major vascular structures [THYM-A]. |
Supportive CareClick to collapse
All patients with thymoma should be evaluated clinically for signs of myasthenia gravis and other paraneoplastic syndromes with appropriate workup and treatment [THYM-1, footnote a]. Patients should be assessed for distress using the NCCN Distress Thermometer and Problem List, which includes social determinants of health [THYM-1, footnote c]. Care should be managed by a multidisciplinary team with experience in management of thymomas and thymic carcinomas [THYM-2]. The team may include radiation oncologists, thoracic surgeons, medical oncologists, neurologists, pathologists, and diagnostic imaging specialists [MS-4].
The source document does not provide specific nutritional support recommendations for thymic malignancies. Standard supportive care for patients undergoing systemic therapy should be applied.
The source document does not provide specific antiemetic protocol recommendations. Standard antiemetic guidelines for the chemotherapy regimens used (platinum-based combinations) should be followed.
The source document does not provide specific G-CSF guidance. Supportive care should follow standard guidelines for the chemotherapy regimens employed.
The source document does not provide specific VTE prophylaxis recommendations for thymic malignancies.
The source document does not provide specific pain management recommendations. Standard supportive pain management should be applied based on disease stage and treatment-related symptoms.
Patients should be assessed for distress. Refer to the NCCN Distress Thermometer and Problem List within the NCCN Guidelines for Distress Management (DIS-A) [THYM-1, footnote c]. Social determinants of health should be included in the distress assessment.
The source document does not provide specific dental care recommendations.
PrognosisClick to collapse
Thymomas and thymic carcinomas are rare thymic epithelial tumors originating in the thymus. Among generally rare tumors of the anterior mediastinum, thymomas are the most common primary tumors, occurring in approximately two per million per year in the United States [4]. Thymic carcinomas are even less common, with an estimated annual incidence of 0.48 per million in the United States [4]. Thymomas are less likely to be invasive and metastasize compared to thymic carcinomas [5-8]. The 5-year survival rate of patients with thymomas is approximately 90% [5,12,13], while the 5-year survival rates for patients with thymic carcinoma are closer to 60% [5,10]. It has been reported that the incidence of thymomas is higher among certain racial and ethnic subgroups, including Black and Asian individuals [3,122]. Patients with thymic carcinomas often present with advanced or metastatic disease at diagnosis [6,9-11]. Many patients with thymic carcinoma may have advanced or metastatic disease at presentation; in two separate studies, over three-quarters of patients with thymic carcinoma were diagnosed with Masaoka stage III or IV disease [9,10].
By Stage
| Stage | Five Yr Survival | Context |
|---|---|---|
| Thymoma - Masaoka Stage I (resected) | ~90% | 10-year survival rate approximately 90% for patients with completely resected Masaoka stage I thymoma [137]. Patients with completely resected stage I thymoma and no capsular invasion are at low recurrence risk and do not require adjuvant therapy [22,91,93,95,96]. |
| Thymoma - Masaoka Stage II (resected) | ~70% | 10-year survival rate approximately 70% for completely resected stage II thymoma [137]. There are conflicting data on whether patients with stage II thymoma with complete resection will derive benefit from postoperative radiation [91,93,95,96,141]. |
| Thymoma - Masaoka Stage III (resected) | ~55% | 10-year survival rate approximately 55% for completely resected stage III thymoma [137]. Higher stage thymomas have a greater risk of disease recurrence and therefore postoperative therapy may be warranted even after complete resection [91,92,95,142,143]. |
| Thymoma - Masaoka Stage IVa (resected) | ~35% | 10-year survival rate approximately 35% for completely resected stage IVa thymoma [137]. The National Cancer Data Base study found that postoperative RT was associated with longer survival, particularly among those with Masaoka-Koga stage IIB and III disease [91]. |
| Thymoma - R0 resection (all stages) | None | 10-year survival rate of patients with thymoma and complete resection was significantly higher than those with incomplete resection or biopsy (76% vs 28%) [56]. Complete resection is considered an important prognostic factor [12,56-60]. |
| Thymic Carcinoma - R0 resection | 60%-70% | The 5-year survival rate of patients who have an R0 resection for thymic carcinoma is estimated to be around 60% to 70% [9,10]. Among patients with thymic carcinoma, the 5-year survival rate of those with complete resection (66.9%) was higher than those with subtotal resection (30.1%) or inoperable disease (24.2%) [5]. |
| Thymic Carcinoma - All stages | ~60% | The 5-year survival rates for thymic carcinoma are closer to 60% overall [5,10]. In a retrospective analysis of 1042 patients, the cumulative incidence of recurrence at 5 years was 35%, while the 10-year cumulative incidence of recurrence was 40% [10]. |
Prognostic Factors
- Completeness of resection (R0 vs R1 vs R2) - R0 resection is an important prognostic factor; 10-year survival 76% with complete resection vs 28% with incomplete resection or biopsy [12,56-60]
- Masaoka-Koga stage - Higher stages have greater risk of recurrence; survival decreases with advancing stage [5,7,39-43]
- Histologic subtype - Thymic carcinoma carries worse prognosis than thymoma [5,10]
- Age - Thymic carcinomas occur over a wide age range including adolescents, while thymomas typically occur in adults [9,11,121]
- Paraneoplastic syndromes - Presence may impact surgical management timing [126-130]
Follow UpClick to collapse
Post Curative Treatment
For patients with completely resected Masaoka-Koga stage I thymoma (no capsular invasion), surveillance should include chest CT with contrast every 6 to 12 months for 2 years, then annually until year 10 [THYM-3]. For all other patients with thymoma, surveillance should include chest CT with contrast every 6 months for 2 years, then annually until year 10 [THYM-3]. For patients with completely resected Masaoka-Koga stage I thymic carcinoma (no capsular invasion), surveillance imaging should consist of chest CT with contrast every 6 to 12 months for 2 years, then annually until 5 years [THYM-3, THYM-4]. For all other patients treated for thymic carcinoma, surveillance should include chest CT every 3 to 6 months for 2 years, then annually for 5 years [THYM-3, THYM-4]. The duration, frequency, and type of imaging for surveillance have not been prospectively evaluated for either thymoma or thymic carcinoma [THYM-3, THYM-4]. The duration for surveillance has not been established [footnote n].
Surveillance Rationale
Despite excellent survival rates, surveillance remains essential for patients with thymoma as a wide range of recurrence rates has been reported [5,56,159]. Late recurrences occurring ≥10 years after surgical resection have been documented for thymoma, which may be due to the indolent growth of some thymomas [56]. For thymic carcinoma, the aggressive nature of the disease places patients at higher risk of recurrence; in one study, 51.2% of patients with thymic carcinoma developed disease recurrence compared with 7.8% of patients with thymoma [5]. A wide range of time to recurrence has been reported; one study reported time to recurrence ranged from 2 to 108 months, with a median of 11 months [9]. Progression to distant sites may occur more frequently in thymic carcinoma than thymoma [13]. Patients with thymoma have an increased risk for second malignancies, although no particular screening studies are recommended [3,4,183,184].
Late Effects Screening
- Cardiac toxicity monitoring - Given younger patient population and long-term survival, cardiac sequelae from RT are a concern. Heart dose should be minimized to reduce long-term cardiac effects [THYM-B 2 of 3].
- Second malignancy screening - Patients with thymoma have increased risk for second malignancies; however, no particular screening studies are recommended [3,4,183,184].
- Paraneoplastic syndrome monitoring - Patients with thymoma should be evaluated for signs of myasthenia gravis and other paraneoplastic syndromes at follow-up [THYM-3, footnote a].
- Respiratory function monitoring - Bilateral phrenic nerve resection should be avoided to prevent severe respiratory morbidity; patients who have undergone phrenic nerve-related surgery should be monitored [THYM-A].
Recurrence Patterns
Thymomas have a propensity for limited metastatic recurrences over long periods, especially in the pleura [MS-8]. As thymoma disease progression is often locoregional (pleural or pulmonary) rather than extrathoracic, surgery or RT may be considered if clinically feasible [13,56,160-163]. For thymic carcinoma, cumulative incidence of recurrence at 5 years was 35% and at 10 years was 40% [10]. One study found that 51.2% of patients with thymic carcinoma developed disease recurrence compared with 7.8% of patients with thymoma [5]. Spread to distant sites including brain, liver, bone, and lung has been documented for thymic carcinoma [13,185].
Key TrialsClick to collapse
| Acronym | Full Name | Year | N | Intervention | Comparator | Population | Primary Endpoint | Key Result | Secondary Outcomes | Practice Change | Journal | Interervention |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CAP Intergroup Trial | Cisplatin plus doxorubicin plus cyclophosphamide in metastatic or recurrent thymoma | 1994 | 30 | None | Advanced or recurrent thymoma (29 patients) and thymic carcinoma (1 patient) | Overall response rate | 50% overall response rate (3 complete responses, 12 partial responses) | None | Established CAP as preferred first-line chemotherapy regimen for thymoma [1, THYM-C 1 of 3] | J Clin Oncol | CAP (cyclophosphamide/doxorubicin/cisplatin) | |
| RYTHMIC | RYTHMIC prospective database study | 2018 | None | Systemic therapy per RYTHMIC protocol | None | Advanced thymoma and thymic carcinoma | Objective response rate | CAP was associated with higher objective response rate than other regimens (44% vs 17%) as exclusive systemic therapy in patients with advanced thymoma or thymic carcinoma | None | Supported CAP as preferred first-line regimen [158] | J Thorac Oncol | |
| WJOG4207L | Multicenter phase II study of carboplatin and paclitaxel for advanced thymic carcinoma | 2015 | 39 | Carboplatin/paclitaxel | None | Chemo-naïve advanced thymic carcinoma | Overall response rate | 36% overall response rate (1 complete response, 13 partial responses); median PFS 7.5 months; 2-year OS 71% | Median progression-free survival 7.5 months; 2-year overall survival 71% | Established carboplatin/paclitaxel as preferred first-line regimen for thymic carcinoma [3, THYM-C 1 of 3] | Ann Oncol | |
| None | Phase II study of carboplatin and paclitaxel in advanced thymoma and thymic carcinoma | 2011 | None | Carboplatin/paclitaxel | None | Advanced thymoma and thymic carcinoma | Response rate and safety | Demonstrated activity of carboplatin/paclitaxel in thymic malignancies | None | Supported use of carboplatin/paclitaxel for thymoma and thymic carcinoma [2] | J Clin Oncol | |
| RELEVENT | RELEVENT phase II trial of ramucirumab plus carboplatin and paclitaxel in untreated metastatic thymic carcinoma | 2024 | 35 | None | Treatment-naïve advanced or metastatic thymic carcinoma | Objective response rate | ORR 80% by investigator assessment and 57.6% by central review; median OS 43.8 months at median follow-up 31.6 months | Median overall survival 43.8 months | Added carboplatin/paclitaxel + ramucirumab as preferred first-line option for thymic carcinoma [8, THYM-C 1 of 3] | Ann Oncol | Carboplatin/paclitaxel + ramucirumab | |
| S1701 | Randomized phase 2 trial of carboplatin-paclitaxel with and without ramucirumab in thymic carcinoma | 2024 | 21 | Carboplatin/paclitaxel | Unresectable, locally advanced, metastatic, or recurrent thymic carcinoma | Response rate | Carboplatin/paclitaxel + ramucirumab had higher response rate than carboplatin/paclitaxel (88% vs 40%) | None | Supported addition of ramucirumab to carboplatin/paclitaxel [198] | JTO Clin Res Rep | Carboplatin/paclitaxel + ramucirumab | |
| MARBLE | Activity and safety of atezolizumab plus carboplatin and paclitaxel in advanced or recurrent thymic carcinoma | 2025 | 48 | None | Advanced or recurrent thymic carcinoma | Objective response rate | 56% objective response rate | Activity and safety profile characterized | Added carboplatin/paclitaxel + atezolizumab as other recommended first-line option for thymic carcinoma [9, THYM-C 1 of 3] | Lancet Oncol | Carboplatin/paclitaxel + atezolizumab | |
| None | Phase II study of everolimus in thymoma and thymic carcinoma previously treated with cisplatin-based chemotherapy | 2018 | None | None | Pretreated thymoma and thymic carcinoma | Response rate | Demonstrated activity of everolimus as subsequent therapy in both thymoma and thymic carcinoma | Safety and tolerability | Established everolimus as preferred subsequent therapy for both thymoma and thymic carcinoma [10, THYM-C 2 of 3] | J Clin Oncol | Everolimus | |
| CAP-GEM | Phase II study of capecitabine and gemcitabine in metastatic pretreated thymic epithelial tumors | 2010/2014 | None | Capecitabine/gemcitabine | None | Metastatic pretreated thymic epithelial tumors | Response rate | Demonstrated activity of capecitabine/gemcitabine combination; final analysis confirmed results | Safety profile | Established gemcitabine/capecitabine as preferred subsequent therapy for thymoma and thymic carcinoma [11,12, THYM-C 2 of 3] | Ann Oncol / Future Oncol | |
| None | ECOG Phase II trial of octreotide ± prednisone in thymoma and thymic carcinoma | 2004 | None | None | Advanced thymoma and thymic carcinoma | Response rate | Activity demonstrated in octreotide-avid disease | Safety and tolerability | Established octreotide ± prednisone as preferred subsequent therapy for thymoma when octreotide/dotatate PET-CT positive [13, THYM-C 2 of 3] | J Clin Oncol | Octreotide ± prednisone | |
| None | Phase II study of pemetrexed in recurrent thymoma and thymic carcinoma | 2018 | None | Pemetrexed | None | Recurrent thymoma and thymic carcinoma | Response rate | Demonstrated activity of pemetrexed as subsequent therapy | Safety profile | Established pemetrexed as preferred subsequent therapy for thymoma [15, THYM-C 2 of 3] | J Thorac Oncol | |
| REMORA | Lenvatinib in advanced or metastatic thymic carcinoma | 2020 | 42 | None | Metastatic or recurrent thymic carcinoma | Objective response rate | ORR 38%; median OS 28.3 months; 36-month OS rate 35.7% | Median overall survival 28.3 months; 36-month OS 35.7% [205] | Established lenvatinib as preferred subsequent therapy for thymic carcinoma [20, THYM-C 2 of 3] | Lancet Oncol | Lenvatinib | |
| None | Pembrolizumab in patients with thymic carcinoma (phase 2 study) | 2018 | None | None | Thymic carcinoma | Objective response rate | ORR 22.5%; durable responses reported [201,204] | Durable responses; high rate of immune-related adverse events (15% severe) | Established pembrolizumab as preferred subsequent therapy for thymic carcinoma with monitoring for immune-related adverse events [21, THYM-C 2 of 3] | Lancet Oncol | Pembrolizumab | |
| STYLE | Phase 2 trial of sunitinib in type B3 thymoma or thymic carcinoma | 2023 | 28 | None | Advanced or recurrent type B3 thymoma and thymic carcinoma (assessable patients) | Overall response rate | ORR 21.4% among 28 assessable patients with thymic carcinoma; median OS 27.8 months | Median overall survival 27.8 months | Supported sunitinib as preferred subsequent therapy for thymic carcinoma [23, THYM-C 2 of 3] | J Thorac Oncol | Sunitinib | |
| None | Sunitinib in chemotherapy-refractory thymoma and thymic carcinoma (phase 2) | 2015 | 23 | None | Chemotherapy-refractory thymoma and thymic carcinoma | Response rate | Partial response in 6/23 patients (26%) with thymic carcinoma | Activity regardless of c-Kit mutation status | Established sunitinib for chemotherapy-refractory thymic carcinoma regardless of c-Kit status [22, THYM-C 2 of 3] | Lancet Oncol | Sunitinib | |
| CAVEATT | Avelumab plus axitinib in unresectable or metastatic type B3 thymomas and thymic carcinomas | 2022 | 32 | None | Advanced thymic carcinoma or type B3 thymoma progressing after ≥1 line of platinum-containing chemotherapy (27 had thymic carcinoma) | Overall response rate | ORR 34% overall; lower in prior anti-angiogenic users (15% vs 47% without prior anti-angiogenic); final median OS 23.4 months; 24-month OS rate 48.5% [208] | Median overall survival 23.4 months; 24-month OS 48.5% | Added axitinib + avelumab as other recommended subsequent therapy for thymic carcinoma [24, THYM-C 2 of 3] | Lancet Oncol | Axitinib + avelumab | |
| Phase 2 IMRT + EP | Intensity modulated radiation therapy plus etoposide/cisplatin for limited advanced unresectable thymic epithelial tumors | 2020 | 56 | None | Limited advanced unresectable thymic epithelial tumors | Objective response rate | 85.7% objective response rate | Safety and tolerability | Supported concurrent chemoradiation as effective treatment for unresectable thymic epithelial tumors [98] | Int J Radiat Oncol Biol Phys | IMRT + concurrent etoposide/cisplatin | |
| None | Phase II study of multidisciplinary approach with induction chemotherapy, surgery, RT, and consolidation chemotherapy for unresectable malignant thymomas | 2004 | None | Induction chemotherapy → surgery → RT → consolidation chemotherapy | None | Unresectable malignant thymomas | Response rate and outcomes | Demonstrated feasibility and efficacy of multimodal approach | Long-term outcomes | Supported multimodal approach for unresectable thymoma [4] | Lung Cancer |
Clinical PearlsClick to collapse
- Pearl 1: Completeness of resection is the most important prognostic factor for thymic malignancies: 10-year survival with complete resection was 76% versus 28% with incomplete resection or biopsy [12,56-60].
- Pearl 2: Avoid transpleural biopsy if thymoma is suspected - this risks converting a stage I thymoma to stage IV by seeding tumor within the pleural space [THYM-A, 132,138].
- Pearl 3: PD-1/PD-L1 inhibitors are not recommended in thymoma (71% grade ≥3 immune-related adverse events including myocarditis) and carry higher risk of myocarditis in thymic carcinoma (5%-9% grade 3-4) compared to other malignancies [180-182].
- Pearl 4: Bilateral phrenic nerve resection should be avoided during thymectomy due to severe respiratory morbidity [THYM-A].
- Pearl 5: Thymic carcinomas are distinct from thymomas with different immunohistochemical and genetic features, more aggressive behavior, and different treatment approaches including systemic therapy options [1,2,18,188].
- Pearl 6: When assessing a mediastinal mass, chest MRI is superior to CT for discriminating thymic malignancy from thymic cyst or hyperplasia, potentially avoiding unnecessary thymectomy [36].
- Pearl 7: Minimally invasive thymectomy is acceptable if performed at specialized centers with experienced surgeons and if all oncologic principles of open thymectomy can be met [THYM-A, 71-84].
- Pearl 8: Patients with thymoma have increased risk for second malignancies, although no particular screening studies are currently recommended [3,4,183,184].
- Pearl 9: All patients should be treated by a multidisciplinary team with experience in thymomas and thymic carcinomas, including thoracic surgeons, radiation oncologists, medical oncologists, neurologists, pathologists, and diagnostic imaging specialists [THYM-2].
- Pearl 10: Postoperative surveillance duration differs between thymoma (through year 10) and thymic carcinoma (through year 5), with thymic carcinoma requiring more frequent imaging (every 3-6 months vs 6-12 months for the first 2 years) [THYM-3, THYM-4].