An official website of the United States government
Home
SEER Inquiry System - Report
Produced: 03/17/2026 1:51 PM
Question 20190077
Inquiry Details
References:
#1: 2018 Summary Stage
#2: 2018 EOD Manual. https://staging.seer.cancer.gov/
Question:
Summary Stage 2018/EOD 2018--Thymus: How should SEER Summary Stage 2018 be coded for a 2018 thymus primary which has mediastinal fat invasion without mediastinal pleural involvement? See Discussion.
Discussion:
The Extent of Disease (EOD) manual states that "Confined to thymus WITH mediastinal or pleural involvement" should be coded as regional by direct extension. I have EOD primary tumor coded as 200 and based on SEER*RSA, this is localized.
Answer:
Code 200 derives Regional Extension (RE) for Summary Stage; however, based on the information you provided, thymus primary with mediastinal fat invasion without mediastinal pleural involvement, EOD Primary Tumor would be coded to 100: Confined to thymus (encapsulated tumor), which includes extension into the mediastinal fat; No mediastinal or pleura involvement. This derives "Localized" for Summary Stage. Per AJCC T1, extension into the mediastinal fat is separate from involvement of the mediastinal pleura.
For Summary Stage 2018, this would be code 1, Localized only (localized, NOS): Confined to thymus, NOS; No mediastinal or pleura involvement or UNKNOWN if involved.
We will note that "extension into the mediastinal fat" is included in code 100 for the next release (September 2020).
