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Clinical calculator summary

1994 Masaoka-Koga Thymoma Stage

A six-category historical surgical-pathological classification of primary thymoma extent.

Evidence-based context for fast calculator use

Purpose:
Reproduce the Koga-modified Masaoka stage from adequately confirmed operative and pathology findings.
Population:
Patients with primary thymoma undergoing adequate surgical and pathological assessment.
Factors:
Capsular relationship, Perithymic extension, Neighboring-organ invasion, Separate pleural/pericardial nodules, Nodal or distant spread
Reference:
Koga et al. Pathol Int. 1994;44:359-367; clarified by ITMIG 2011.
HomeMasaoka-Koga Staging (Thymoma)
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Masaoka-Koga Staging (Thymoma)

Clinical Context & Background

This calculator implements the 1994 Koga modification of the 1981 Masaoka system, interpreted using the 2011 International Thymic Malignancy Interest Group clarification. Select the highest applicable stage supported by operative and microscopic findings.
It is historical surgical-pathological staging for primary thymoma, not definitive preoperative clinical staging, recurrence staging, current AJCC/UICC TNM staging, an individualized prognosis, or a treatment-selection algorithm. If reported, Masaoka-Koga should accompany rather than replace current TNM classification. Adequate sampling and microscopic confirmation are important; limited biopsy and previously treated tumors require caution.
Primary Source EvidenceMasaoka A, et al. Cancer. 1981;48:2485-2492. Koga K, et al. Pathol Int. 1994;44:359-367. Detterbeck FC, et al. J Thorac Oncol. 2011;6:S1710-S1716.
Formula Logic
Assign the highest applicable 1994 Masaoka-Koga stage from the surgically and microscopically confirmed extent of primary thymoma: I, IIA, IIB, III, IVA, or IVB.

Reference Data

Stage1994 Koga / 2011 ITMIG definition
ICompletely encapsulated; includes invasion into but not through the capsule, or absent capsule without surrounding-tissue invasion
IIAMicroscopic transcapsular invasion not grossly apparent
IIBGross, microscopically confirmed extension into normal thymus/perithymic fat; or pleural/pericardial adherence requiring resection without microscopic invasion
IIIMicroscopically confirmed invasion of pleura, pericardium, lung, nerves, major vessels, or another neighboring organ
IVASeparate, microscopically confirmed pleural, pericardial, or epicardial tumor nodules
IVBAny nodal involvement or hematogenous/distant metastasis, including separate intraparenchymal pulmonary metastasis

Clinical Workflow

Use, Interpret, And Continue The Patient Pathway

Expand for workflow guidance, limitations, examples, and related next steps.

When To Use

  • For primary thymoma after adequate operative and pathology assessment.
  • Select the highest applicable category when more than one confirmed finding is present.

How To Interpret

  • Stages I-IIB describe encapsulation or limited capsular/perithymic extension.
  • Stage III is direct microscopically confirmed neighboring-structure invasion; IVA is separate serosal nodules; IVB is nodal or hematogenous/distant spread.

What To Do Next

  • Document the operative and microscopic findings supporting the assigned category.
  • Report current TNM classification separately and integrate all findings in multidisciplinary review.

Limitations

  • Not definitive preoperative staging, recurrence staging, individualized prognosis, or a treatment rule.
  • Limited biopsy, prior treatment, or incomplete pathological confirmation may make the category unassignable.
  • Contemporary CAP reporting prioritizes current TNM; Masaoka-Koga should not replace it.

Validated Population

Primary thymoma with adequate surgical and pathological assessment in the historical source context.

Separate pleural nodule

A separate microscopically confirmed pleural tumor nodule is Stage IVA, whereas direct pleural invasion is Stage III.

Calculation verification history

Verified

  1. : Production browser revalidation

    • Five source-backed Masaoka-Koga cases were exercised on the public production route through visible controls; 5/5 expected stages matched across I, IIA, IIB, III, and IVB.
    • No unexpected N/A, literal undefined value, stale control, or browser-console error was observed.
    Download latest production check (Excel)

    Case-level evidence is retained in validation/browser-revalidation/masaoka-thymoma-staging-2026-08-03.json.

  2. : Local browser remediation verified; production retest pending

    • Ten source-backed cases passed through visible controls across 11 submissions, covering all six Masaoka-Koga stages, repeated selections, missing selection, and reset/repeat.
    • Every valid result displayed its highest confirmed extent with a neutral published-rule decision; no literal undefined value appeared.
    • The original production UI and hydration findings remain open until deployment and public revalidation.

    Case-level local remediation evidence is retained in validation/browser-production/masaoka-thymoma-staging.local-remediation.json.

  3. : Production browser validation

    • Ten source-backed cases were exercised on the public production route through visible browser controls; 1/10 case records passed their expected-versus-observed assertions across 11 visible submissions.
    • Overall browser status: failed-ui-and-console. high: Every rendered stage displayed literal `undefined` below the Highest confirmed extent narrative in the visible trace. | medium: Production emitted minified React error #418 during route loads/reloads used by this run.
    • Case-level inputs, expected and observed results, reset/repeat behavior, failure reproductions, and console evidence are retained in the production-browser evidence record.

    Case-level production evidence is retained in validation/browser-production/masaoka-thymoma-staging.json.

  4. : Full validation test

    • 192/192 source-category, definition, UI, trace, malformed-input, scope, registry, report, history, and isolation checks passed.
    • This verifies implementation of the selected historical stage system, not independent clinical validation, current TNM staging, prognosis, or treatment selection.

  5. : Definition and input-contract correction

    • Completed the Stage I-IVB definitions using the Koga modification and ITMIG clarification, including capsular nuance, adherence, direct invasion, separate nodules, nodal disease, and pulmonary metastasis.
    • Removed the Stage I default and treatment directives; now requires one exact explicit category and returns Invalid Input for missing, extra, malformed, or unsupported values.

Verification confirms the calculator implementation against the cited model; it is not independent clinical validation, regulatory approval, or medical advice.

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Frequently Asked Questions

Does Masaoka-Koga replace current TNM staging?

No. It remains frequently used historically, but should accompany rather than replace contemporary AJCC/UICC TNM classification.

Can this be assigned from imaging alone?

Not definitively. The system is surgical-pathological and several categories require microscopic confirmation.

Does the stage automatically determine treatment?

No. The stage is one part of multidisciplinary assessment and is not an autonomous treatment-selection rule.

Evidence-based oncology decision support. Verify with clinical guidelines.