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SEER Inquiry System - Report
Produced: 02/06/2026 2:15 AM
Question 20210071
Inquiry Details
References:
#1: WHO Class Breast Tumors. 5th edition; online version
#2: ICD-O-3.2
Question:
Solid Tumor Rules (2018/2021)/Histology--Breast: How is histology coded for a diagnosis of invasive mammary neuroendocrine tumor (NET), grade 2/3? See Discussion.
Discussion:
Table 3 (Breast Equivalent Terms and Definitions) lists “Neuroendocrine tumor, well-differentiated” of the breast as histology 8246/3. There is no entry for a grade 2 neuroendocrine tumor of the breast in Table 3.
The pathologist did not indicate the neuroendocrine tumor was poorly differentiated (or it would otherwise be a small cell carcinoma). The pathologist noted “By current WHO criteria, this tumor is characteristic of a mammary neuroendocrine tumor, grade 2. These invasive tumors have similar prognostic and predictive features of invasive ductal carcinoma of the same grade and stage.”
Answer:
Assign code 8249/3, neuroendocrine tumor, grade 2 based on the pathologist statement of mammary neuroendocrine tumor grade 2. According to WHO Classification of Tumors of the Breast, 5th edition, neuroendocrine tumor (NET) is an invasive tumor characterized by low/intermediate grade.
If the histology term is not listed in the Solid Tumor rules, the instructions state to also check ICD-O and updates. Per ICD-O, NET, grade 2 is coded 8249/3. Breast Table 3 will be updated for 2023.
