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SEER Inquiry System - Report
Produced: 10/13/2025 2:43 PM
Question 20230023
Inquiry Details
References:
#1: Solid Tumor Rules. Malignant CNS, March 2023 update
#2: WHO Class CNS Tumors, 406-414. 5th edition
Question:
Solid Tumor Rules/Multiple Primaries—Brain and CNS: How many primaries are accessioned, and which M Rule applies, to a 2018 pituitary adenoma (8272/0) that was partially resected followed by a 2023 resection of residual disease proving pituitary adenoma/pituitary neuroendocrine tumor (8727/3)? See Discussion.
Discussion:
The patient had residual tumor following the 2018 transsphenoidal resection and underwent an additional surgery after the residual tumor increased in size. Since pituitary adenoma/pituitary neuroendocrine tumor (PitNET) is a new malignant neoplasm for cases diagnosed 2023 and later, should this be a new primary per M5? Or do we disregard the change in behavior and apply rule M2 (single tumor is a single primary) for this scenario?
Answer:
This case does not fall into the standard rules. WHO criteria for diagnosing pituitary adenoma have recently changed (per 5th Ed WHO CNS book) and we will likely see more PitNET’ s than pituitary adenomas in the future. PitNET may be invasive or non-invasive but the likelihood of the pathologists providing this information is low. Since we don’t know if the 2018 adenoma was a PitNET based on current criteria or if it transformed to the malignant neoplasm, err on the side of caution and abstract a second primary per M5.
This issue is new, and we’ve received numerous questions concerning pathologist reviewing older cases of pituitary adenoma and reclassifying them as PitNET using the new criteria.
