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SEER Inquiry System - Report
Produced: 03/31/2026 7:24 AM
Question 20230062
Inquiry Details
References:
2018 EOD Manual. Appendix-8th, V9: EOD Primary Tumor; EOD Mets
Question:
Update to current manual/EOD 2018/EOD Primary Tumor--Appendix: Is it correct to code Extent of Disease (EOD) Primary Tumor as code 500 (Invasion of/through serosa (mesothelium) (visceral peritoneum)) and EOD Mets as code 30 (Intraperitoneal metastasis (peritoneal carcinomatosis) WITH or WITHOUT peritoneal mucinous deposits containing tumor cells), when the resection pathology report for a low-grade appendiceal mucinous neoplasm (LAMN) proves “Tumor Extent: Acellular mucin invades visceral peritoneum (serosa)” as well as metastatic LAMN within the right lower quadrant peritoneum? See Discussion.
Discussion:
This patient had serosal involvement and the pathologist and managing physician staged this as pT4a disease. This extension seems best captured by EOD Primary Tumor code 500. Additionally, the patient had discontinuous metastatic involvement of the peritoneum, and this was staged by the pathologist and managing physician as pM1b (Intraperitoneal metastasis only, including peritoneal mucinous deposits containing tumor cells). Although this peritoneal involvement was present in the right lower quadrant, it was staged as distant metastatic disease and not as part of the primary tumor category. However, currently EOD Primary Tumor code 600 would seem to apply since the peritoneal tumor was in the right lower quadrant. Code 600 is defined as mucinous tumors with peritoneal involvement confined within right lower quadrant. This EOD Primary Tumor code and the physician’s M category assignment do not align; the physician has staged this as distant metastasis (M category, not the T category). Should the peritoneal metastasis (even limited to the right lower quadrant) be included in the EOD Mets field and not in the EOD Primary Tumor field? In other words, should the peritoneal involvement included in EOD Primary Tumor code 600 be reclassified in EOD Mets code 30 (Intraperitoneal metastasis (peritoneal carcinomatosis) WITH or WITHOUT peritoneal mucinous deposits containing tumor cells)?
Answer:
Assign code 500 for EOD Primary Tumor and code 30 for EOD Mets. This will correctly derive the T4aM1b stage based on AJCC 8th edition.
Abstraction of peritoneal metastasis changed from the T category in the AJCC 7th edition to the M category in the 8th and 9th AJCC editions. As a result, for cases diagnosed in 2018 and later, peritoneal deposits in the right lower quadrant should be abstracted as EOD Primary Tumor code 500 and EOD Mets code 30. However, the EOD Primary Tumor code of 600 has not yet been updated to align with the 8th and 9th AJCC editions. The 2025 updates will correct for this via a conversion for cases diagnosed in 2018 and forward where EOD Primary Tumor = 600 and EOD Mets = 00 or 10 to EOD Primary Tumor = 500 and EOD Mets = 30. Effective immediately, abstract peritoneal deposits in the right lower quadrant as EOD Primary Tumor code 500 and EOD Mets code 30, even though you will still have the ability to assign EOD Primary Tumor code 600 in your abstraction software until the 2025 updates are deployed.
