# Type B3 thymoma

Source: https://onco.cc/cancers/thymoma-type-b3/  
OnCo record `thymoma-type-b3` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Type B3 thymoma is the most aggressive thymoma, a thymus gland tumour made mostly of epithelial cells with few lymphocytes, sitting at the border with thymic carcinoma. More than a third have already grown into the chest structures when found, so it is treated with surgery plus radiotherapy, and chemotherapy before surgery when it is too large to remove at once.

## Summary

Type B3 thymoma is the epithelial-rich thymoma of the WHO classification, once called well-differentiated thymic carcinoma; the ITMIG consensus set criteria separating B3 from B2 and from thymic carcinoma, the latter distinguished by frank cytological atypia, loss of thymus-like features and expression of CD5 and CD117 (Marx 2014). In the worldwide database, 38 percent of type B3 thymomas were stage III at diagnosis, the highest of any type, and the B1 to B3 group recurred in 2 to 7 percent after resection against 1 to 2 percent for A and AB (Weis 2015).

How it differs from its parent: it is the thymoma most likely to invade the pericardium, great vessels and lung and to recur, so it is the one where preoperative chemotherapy, radical surgery with vascular reconstruction and postoperative radiotherapy are most often combined, and the one that must be separated from thymic carcinoma, which has its own page and its own drugs.

How common: the ITMIG database gives its stage distribution but not its share in the abstract read; it is less common than B2 (Weis 2015).

Treatment: complete resection when feasible with postoperative radiotherapy for stage II to III disease or incomplete resection; induction platinum-based chemotherapy (cisplatin, doxorubicin, cyclophosphamide) for tumours not resectable at presentation, then surgery or radiotherapy; systemic therapy for recurrence as on the parent page.

## Fields

- Kind: Cancer
- Last checked: 2026-09-24
- Also known as: Type B3 thymoma (epithelial-rich, the most aggressive thymoma); Well-differentiated thymic carcinoma (historical term); Epithelial thymoma; Atypical thymoma
- Tags: subtype-page; wave4; rare
- Group: thoracic
- Burden: A minority of thymomas but the one most often advanced: 38 percent of type B3 in the ITMIG worldwide database presented at stage III (Weis 2015).
- Subtypes: Type B3 thymoma, encapsulated (stage I to II); Type B3 thymoma, locally invasive (stage III; 38 percent); Combined B3 thymoma and thymic carcinoma (classified by the carcinoma component)
- Biomarkers: WHO histotype on ITMIG criteria; absence of CD5 and CD117 (thymic carcinoma markers); Masaoka-Koga or TNM stage and resection status; Acetylcholine receptor antibodies (myasthenia gravis); Ki-67 and mitoses

## Sections of this record

The page is a hub with ten sections in reading order; large sections have their own page. The same plan as JSON: https://onco.cc/api/v1/cancers/thymoma-type-b3/sections.json

- Overview (on the hub): The TL;DR, the family this cancer belongs to, the organ, who gets it and what the state of the art is. https://onco.cc/cancers/thymoma-type-b3/#overview
- What it is (on the hub): Anatomy, the subtypes and how they differ, how it is staged, and where advanced disease spreads. https://onco.cc/cancers/thymoma-type-b3/#what-it-is [3 subtypes]
- Finding it (on the hub): How it shows itself, how it is confirmed, what screening exists, and the biomarkers clinicians test for. https://onco.cc/cancers/thymoma-type-b3/#finding-it [4 biomarkers]
- Treating it (on the hub): The standard of care by setting, the medicines, surgery and radiotherapy named in it, and the regimens behind them. https://onco.cc/cancers/thymoma-type-b3/#treating-it [1 setting, 1 decision with options]
- Evidence (on the hub): Trials recruiting now, the landmark trials, the key papers and what they mean, the latest literature, and the milestones year by year. https://onco.cc/cancers/thymoma-type-b3/#evidence
- The science (on the hub): The molecular landscape: the targets and how often each appears, the pathways, the mechanics stages and the preclinical models. https://onco.cc/cancers/thymoma-type-b3/#science
- Where you are (own page): Cases by country, the UK and NHS pathway and other country lenses, and the expert centres with trials on record. https://onco.cc/cancers/thymoma-type-b3/where-you-are/
- Living with it (on the hub): The decisions you may face, the aids that walk through them, the warnings on record, the first sixty days and the questions to ask. https://onco.cc/cancers/thymoma-type-b3/#living-with-it [8 questions, 5 red cards]
- What is coming (own page): Everything in development, the open problems and what is being done about them, the roadmaps, and what changed on this record. https://onco.cc/cancers/thymoma-type-b3/coming/ [3 medicines]
- Data (own page): Every connected record, the notes, the JSON, Markdown and RDF twins, and where the record came from and when it was checked. https://onco.cc/cancers/thymoma-type-b3/data/ [9 connected records]

## Standard of care

- All stages: Resection with postoperative radiotherapy for stage II to III or incomplete resection; induction platinum-based chemotherapy for unresectable tumours; recurrence as on the parent page. ([Thymoma (WHO types A, AB, B1, B2 and B3)](https://onco.cc/cancers/thymoma/), [Thymic carcinoma](https://onco.cc/cancers/thymic-carcinoma/), [Cisplatin](https://onco.cc/drugs/cisplatin/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/))

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Thymoma
- NCI PDQ: thymoma and thymic carcinoma treatment: https://www.cancer.gov/types/thymus-cancer/thymoma-thymic-carcinoma
- Weis 2015, JTO: the impact of thymoma histotype on prognosis in the ITMIG worldwide database, 4,221 thymomas: https://doi.org/10.1097/jto.0000000000000393
- Marx 2014, JTO: ITMIG consensus on the use of the WHO histological classification of thymoma and thymic carcinoma: https://doi.org/10.1097/jto.0000000000000154

## Connected records

- cancers: [Thymic carcinoma](https://onco.cc/cancers/thymic-carcinoma/), [Thymoma (WHO types A, AB, B1, B2 and B3)](https://onco.cc/cancers/thymoma/), [Thymoma and thymic carcinoma](https://onco.cc/cancers/thymic-epithelial/), [Type A and type AB thymoma](https://onco.cc/cancers/thymoma-type-a-ab/), [Type B1 and type B2 thymoma](https://onco.cc/cancers/thymoma-type-b1-b2/)
- drugs: [Cisplatin](https://onco.cc/drugs/cisplatin/), [Cyclophosphamide](https://onco.cc/drugs/cyclophosphamide/), [Doxorubicin](https://onco.cc/drugs/doxorubicin/)

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JSON: https://onco.cc/api/v1/entities/thymoma-type-b3.json