# Thymoma (WHO types A, AB, B1, B2 and B3)

Source: https://onco.cc/cancers/thymoma/  
OnCo record `thymoma` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Thymoma is the slower-growing kind of thymic epithelial tumour, an indolent cancer of the thymus gland behind the breastbone that often announces itself through the autoimmune disease myasthenia gravis. Complete surgical removal cures most patients, radiotherapy is added when the tumour has grown through its capsule, and chemotherapy is used to shrink large tumours or control spread in the chest.

## Summary

Thymomas are tumours of thymic epithelial cells mixed with non-neoplastic immature T lymphocytes, classified by the WHO into types A, AB, B1, B2 and B3 by the shape of the epithelial cells and the density of lymphocytes, with B3 the most aggressive and A and AB the most indolent. Type A and AB tumours nearly all carry the GTF2I L424H mutation, a finding unique to thymoma, while B thymomas have few recurrent mutations. Because the thymus educates T cells, thymomas are tied to autoimmunity: about a third of patients have myasthenia gravis, others have pure red cell aplasia, hypogammaglobulinaemia (Good syndrome) or other autoimmune conditions, and acetylcholine receptor antibodies are checked before any operation so that myasthenia can be controlled first. Stage, whether by the Masaoka-Koga system or the TNM system introduced in 2017, and completeness of resection matter more than histology for survival.

Surgery is the treatment. Encapsulated tumours are removed whole with the thymus, increasingly by video-assisted or robotic approaches, and the guidelines advise against preoperative biopsy of a resectable encapsulated mass. Postoperative radiotherapy is recommended for stage III disease and for incomplete resection and considered for stage II B2 to B3 tumours, and unresectable or bulky tumours are given induction chemotherapy with cisplatin, doxorubicin and cyclophosphamide (CAP) or a platinum-etoposide doublet before reassessment for surgery. Pleural spread is treated with repeated resection or, in some centres, pleurectomy. For recurrent disease not amenable to local treatment, chemotherapy is repeated, octreotide with prednisone helps octreotide-scan-positive tumours, everolimus produced disease control in a phase 2 trial, and sunitinib and lenvatinib have activity; PD-1 antibodies are used with great caution because thymoma patients develop severe myocarditis, myositis and other immune toxicity far more often than other cancer patients. Thymoma recurs late and slowly, so follow-up runs for at least ten years.

## Fields

- Kind: Cancer
- Last checked: 2026-09-18
- Also known as: Thymoma; Type A thymoma; Type AB thymoma; Type B thymoma; Thymoma with myasthenia gravis
- Tags: subtype-page; thoracic
- Group: thoracic
- Burden: The commonest tumour of the anterior mediastinum in adults yet rare in absolute terms; most are found at stage I or II, and about a third of patients have myasthenia gravis.
- Subtypes: Type A thymoma (spindle cell, indolent, GTF2I mutant); Type AB thymoma (mixed, indolent, GTF2I mutant); Type B1 thymoma (lymphocyte-rich); Type B2 thymoma; Type B3 thymoma (epithelial-rich, the most aggressive thymoma); Thymoma with myasthenia gravis or other paraneoplastic autoimmunity; Micronodular thymoma with lymphoid stroma (rare, indolent); Stage III to IVA thymoma with pleural spread
- Biomarkers: WHO histotype; Masaoka-Koga and TNM stage; Completeness of resection (R0, R1, R2); Acetylcholine receptor antibodies (myasthenia screen before surgery); GTF2I L424H mutation (type A and AB); Octreotide scan or somatostatin receptor PET (somatostatin analogue eligibility)

## Standard of care

- Diagnosis and staging: Contrast CT of the chest, acetylcholine receptor antibodies and neurology review; no biopsy of a resectable encapsulated mass; MRI to separate thymoma from cysts and hyperplasia. ([CT (computed tomography)](https://onco.cc/technologies/ct/), [MRI](https://onco.cc/technologies/mri/))
- Resectable (stage I to III): Complete thymectomy with the tumour, by sternotomy or minimally invasive or robotic approaches for smaller tumours; en bloc resection of involved pericardium, lung or vessels for stage III. ([Robotic & minimally invasive surgery](https://onco.cc/technologies/robotic-surgery/))
- After surgery: Postoperative radiotherapy for stage III or incomplete resection; considered for stage II B2 to B3 tumours; observation for completely resected stage I and II type A to B1. ([IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Proton therapy](https://onco.cc/technologies/proton-therapy/))
- Unresectable or bulky disease: Induction chemotherapy with cisplatin, doxorubicin and cyclophosphamide (CAP) or a platinum doublet, then surgery or radiotherapy according to response. ([Cisplatin](https://onco.cc/drugs/cisplatin/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/), [Carboplatin](https://onco.cc/drugs/carboplatin/), [Paclitaxel / nab-paclitaxel](https://onco.cc/drugs/paclitaxel/))
- Recurrent or metastatic disease: Repeat resection of pleural recurrences where feasible; chemotherapy rechallenge; octreotide with prednisone for octreotide-scan-positive tumours; everolimus, sunitinib or lenvatinib; PD-1 antibodies avoided or given only in trials because of severe immune toxicity. ([Somatostatin analogues (octreotide, lanreotide)](https://onco.cc/drugs/octreotide-lanreotide/), [Everolimus](https://onco.cc/drugs/everolimus/), [Sunitinib](https://onco.cc/drugs/sunitinib/), [Lenvatinib](https://onco.cc/drugs/lenvatinib/), [Immune-related adverse events (irAEs)](https://onco.cc/terms/irae/), [A Study of KC1036 in Patients with Advanced Thymic Tumors](https://onco.cc/trials/nct05683886/), [Target-Selected CAR-NK Cells (CD30, CD5, or Mesothelin) for Relapsed/Refractory B2 Thymoma or Thymic Carcinoma](https://onco.cc/trials/nct07598955/))

## State of the art

- Complete resection cures most thymomas and minimally invasive thymectomy is now routine for small tumours.
- The 2017 TNM system unified staging across the world's thymic registries.
- Immunotherapy is the one modern treatment largely closed to thymoma patients because of autoimmune toxicity.

## Open problems

- Randomised trials are almost absent; postoperative radiotherapy for stage II disease rests on registry data.
- No systemic therapy is approved specifically for thymoma.
- Autoimmune toxicity keeps checkpoint inhibitors off the table for most patients.
- Late recurrence a decade or more after surgery makes trial endpoints slow.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Thymoma
- NCCN Thymomas and Thymic Carcinomas: https://www.nccn.org/guidelines/guidelines-detail?category=1&id=1469
- ESMO thymic epithelial tumours guideline 2015: https://doi.org/10.1093/annonc/mdv277
- Wikipedia: https://en.wikipedia.org/wiki/Thymoma

## Connected records

- cancers: [Lung neuroendocrine tumours (typical and atypical carcinoid)](https://onco.cc/cancers/lung-net/), [Thymic carcinoma](https://onco.cc/cancers/thymic-carcinoma/), [Thymoma and thymic carcinoma](https://onco.cc/cancers/thymic-epithelial/)
- technologies: [CT (computed tomography)](https://onco.cc/technologies/ct/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [MRI](https://onco.cc/technologies/mri/), [Proton therapy](https://onco.cc/technologies/proton-therapy/), [Robotic & minimally invasive surgery](https://onco.cc/technologies/robotic-surgery/), [Small-molecule kinase inhibitors](https://onco.cc/technologies/kinase-inhibitors/)
- targets: [VEGF / VEGFR](https://onco.cc/targets/vegf/)
- drugs: [Carboplatin](https://onco.cc/drugs/carboplatin/), [Cisplatin](https://onco.cc/drugs/cisplatin/), [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [EB-CAR30-NK](https://onco.cc/drugs/eb-car30-nk/), [Everolimus](https://onco.cc/drugs/everolimus/), [KC1036](https://onco.cc/drugs/kc1036/), [Lenvatinib](https://onco.cc/drugs/lenvatinib/), [Paclitaxel / nab-paclitaxel](https://onco.cc/drugs/paclitaxel/), [Somatostatin analogues (octreotide, lanreotide)](https://onco.cc/drugs/octreotide-lanreotide/), [Sunitinib](https://onco.cc/drugs/sunitinib/)
- terms: [Disease-specific staging and risk systems (FIGO, Ann Arbor, IPI, R-ISS, ELN, IMDC)](https://onco.cc/terms/staging-systems/), [Immune-related adverse events (irAEs)](https://onco.cc/terms/irae/)
- trials: [A Study of KC1036 in Patients with Advanced Thymic Tumors](https://onco.cc/trials/nct05683886/), [Target-Selected CAR-NK Cells (CD30, CD5, or Mesothelin) for Relapsed/Refractory B2 Thymoma or Thymic Carcinoma](https://onco.cc/trials/nct07598955/)
- key papers: [Masaoka staging: follow-up study of thymomas with special reference to their clinical stages](https://onco.cc/key-papers/paper-masaoka-thymoma-clinical-staging-cancer-1981/), [The 2021 WHO classification of tumours of the thymus and mediastinum: what is new in thymic epithelial, germ cell and mesenchymal tumours](https://onco.cc/key-papers/paper-who-2021-thymus-mediastinum-classification-marx-jto-2022/), [Thymic epithelial tumours: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up](https://onco.cc/key-papers/paper-esmo-thymic-epithelial-tumours-guideline-ann-oncol-2015/)

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