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SEER Inquiry System - Report
Produced: 10/30/2025 2:37 AM
Question 20230070
Inquiry Details
References:
Solid Tumor Rules. Breast, 2023 Update; May 2023 Update
Question:
Solid Tumor Rules/Multiple Primaries--Breast: How many primaries should be accessioned for a diagnosis of invasive carcinoma of the left breast (8500/3) in 2020 followed by a 2023 diagnosis of dedifferentiated carcinoma in the left breast (8020/3)? See Discussion.
Discussion:
The WHO Blue Books do not include dedifferentiated carcinoma as a valid histology for the breast. However, there is known to be progression of ductal carcinoma that is essentially dedifferentiation of an estrogen receptor, progesterone receptor, and HER2 breast carcinoma to a triple negative "dedifferentiated" carcinoma which it appears this patient has. Whether we should accession this as a separate 8020/3 primary per M14 is unclear and the Solid Tumor Manual does not address this scenario.
Answer:
Abstract a single primary using Breast Solid Tumor Rules, Rule M18, as none of the previous rules apply.
Undifferentiated carcinoma is a malignant epithelial tumour lacking overt evidence of a specific line of differentiation. Dedifferentiated carcinoma is composed of an undifferentiated carcinoma and a differentiated component. Dedifferentiated carcinoma (8020/3) as a morphology is associated with cancer of the endometrium and ovary rather than the breast. Breast cancer shows a broad spectrum of morphology with extensive variation in histological type and grade, related to the complexity of carcinogenesis. This includes initial genetic changes in the cell of origin, subsequent genetic and epigenetic alterations, and reprogramming that occur at various stages of development along with interaction of other factors that influence the process of differentiation. This scenario likely represents the process of phenotypic change of a carcinoma at a later stage, better known as transdifferentiation.
