# Type B1 and type B2 thymoma

Source: https://onco.cc/cancers/thymoma-type-b1-b2/  
OnCo record `thymoma-type-b1-b2` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Type B1 and type B2 thymoma are thymus gland tumours in which the epithelial tumour cells are mixed with many immature lymphocytes, resembling the normal thymic cortex; B2 is the commonest thymoma of all. They are strongly linked to myasthenia gravis, are usually cured by surgery, and get radiotherapy when they have grown beyond the gland or could not be fully removed.

## Summary

Types B1 and B2 sit between the indolent A and AB thymomas and the aggressive B3 in the WHO classification; B1 resembles normal thymic cortex with sparse epithelial cells and B2 has clusters of epithelial cells among the lymphocytes, and the ITMIG consensus set criteria for distinguishing B1, B2 and B3 (Marx 2014). In the worldwide database type B2 was the most common histotype (28 percent), the B types presented at higher stages than A and AB, and recurrence after resection for B1 to B3 was 2 to 7 percent, with age, stage and resection status the multivariate predictors of survival and histology affecting recurrence (Weis 2015). Myasthenia gravis and other paraneoplastic autoimmunity are most frequent with the B types.

How it differs from its parent: the lymphocyte-rich histology can be mistaken for lymphoma or normal thymus on biopsy, the association with myasthenia gravis shapes perioperative care, and the B types more often present at Masaoka-Koga stage II or III than types A and AB.

How common: B2 is 28 percent of thymomas, the largest share (Weis 2015).

Treatment: complete resection with or without preoperative therapy for locally advanced disease; postoperative radiotherapy for stage III or incomplete resection; platinum-based chemotherapy (cisplatin, doxorubicin, cyclophosphamide) for unresectable or metastatic disease, as on the parent page; myasthenia gravis managed jointly with neurology.

## Fields

- Kind: Cancer
- Last checked: 2026-09-24
- Also known as: Type B1 thymoma; Type B2 thymoma; Lymphocyte-rich thymoma; Cortical thymoma; Type B1 thymoma (lymphocyte-rich)
- Tags: subtype-page; wave4; rare
- Group: thoracic
- Burden: Type B2 is the most common thymoma at 28 percent of 4,221 thymomas in the ITMIG worldwide database; B1 and B2 are more frequent in Asia than types A and AB (Weis 2015).
- Subtypes: Type B1 thymoma (lymphocyte-rich, organoid; indolent); Type B2 thymoma (epithelial cell clusters among lymphocytes; the commonest thymoma); Type B1 or B2 thymoma with myasthenia gravis; Combined B2/B3 thymoma
- Biomarkers: WHO histotype on ITMIG criteria (epithelial cell density); Masaoka-Koga or TNM stage and resection status; Acetylcholine receptor antibodies (myasthenia gravis); Terminal deoxynucleotidyl transferase-positive immature T cells (distinguishes from lymphoma)

## 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-b1-b2/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-b1-b2/#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-b1-b2/#what-it-is [4 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-b1-b2/#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-b1-b2/#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-b1-b2/#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-b1-b2/#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-b1-b2/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-b1-b2/#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-b1-b2/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-b1-b2/data/ [9 connected records]

## Standard of care

- All stages: Complete resection; postoperative radiotherapy for stage III or incomplete resection; platinum-based chemotherapy for unresectable or metastatic disease, as on the parent page. ([Thymoma (WHO types A, AB, B1, B2 and B3)](https://onco.cc/cancers/thymoma/), [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: [Micronodular thymoma with lymphoid stroma](https://onco.cc/cancers/micronodular-thymoma/), [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 B3 thymoma](https://onco.cc/cancers/thymoma-type-b3/)
- 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-b1-b2.json