# Thymic tumour staging (Masaoka-Koga and AJCC chapter 35)

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

## TL;DR

Thymoma has long been staged by the Masaoka-Koga system, which asks whether the tumour has broken through its capsule and into nearby organs; TNM staging from the IASLC and ITMIG is the newer standard.

## Summary

In the NCI's health professional summary, the Masaoka staging system of 1981, modified by Koga in 1994, is the most commonly used and is recommended by ITMIG: stage I, completely encapsulated with no capsular invasion under the microscope; II, invasion into surrounding fat or mediastinal pleura, or microscopic invasion into the capsule; III, invasion into neighbouring organs (pericardium, lung, great vessels); IVa, pleural or pericardial spread; IVb, spread through lymph or blood. For consistency the AJCC and UICC adopted a TNM system developed by the IASLC and ITMIG; AJCC chapter 35 (thymus) has a Version 9 protocol for 2025 in the AJCC 2026 table.

## Fields

- Kind: Term
- Last checked: 2026-11-04
- Also known as: Masaoka-Koga; Masaoka-Koga stage; Masaoka; Masaoka stage; thymoma staging; IASLC/ITMIG thymic staging

## Sources

- National Cancer Institute, Thymoma and thymic carcinoma treatment (PDQ), health professional version: stage information: https://www.cancer.gov/types/thymoma/hp/thymoma-treatment-pdq
- American College of Surgeons, AJCC Current Staging System 2026 (which chapters are 8th edition and which Version 9): https://www.facs.org/media/c5ik5tkr/ajcc-current-staging-system-2026.pdf

## Connected records

- terms: [AJCC Version 9 staging](https://onco.cc/terms/ajcc-version-9/), [Disease-specific staging and risk systems (FIGO, Ann Arbor, IPI, R-ISS, ELN, IMDC)](https://onco.cc/terms/staging-systems/), [ITMIG modified RECIST for thymic tumours](https://onco.cc/terms/itmig-mrecist/), [TNM staging](https://onco.cc/terms/tnm-staging/)
- 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/)

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JSON: https://onco.cc/api/v1/entities/thymus-staging.json