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SEER Inquiry System - Report
Produced: 01/08/2026 4:04 PM
Question 20160075
Inquiry Details
References:
2007 MP/H Rules
Question:
MP/H Rules/Histology--Breast: What histology code(s) and MP/H rule applies for a breast resection final diagnosis of "undifferentiated sarcoma associated with a malignant phyllodes tumor and a tumor size of approximately 7 x 6.5 x 4 cm"? (The tumor is primarily sarcoma, with the phyllodes tumor measuring 2.8 cm)? See Discussion.
Discussion:
Patient has a diagnosis of undifferentiated sarcoma with an associated malignant phyllodes tumor in a single mass. Should this be abstracted as two primaries, one for an undifferentiated sarcoma and the other for a malignant phyllodes tumor? Which MP/H rule applies?
Answer:
Abstract a single primary. Based on the information provided, this is a single tumor, and therefore a single primary, Rule M3. Code the histology to malignant phyllodes tumor.
According to our expert pathologist consultant, "The presence of a phyllodes tumor component identifies the whole thing as such. Stromal overgrowth/sarcoma is the usual identifier of malignancy in a phyllodes tumor. (If there were no phyllodes component we would be left with undifferentiated sarcoma, but that is not the case here. The diagnosis of malignancy in phyllodes tumor may be difficult/problematic when there is no overt stromal/sarcoma overgrowth as in this case.) As an aside, the behaviors of pure sarcoma and a phyllodes tumor such as we have here are similar, but we would lose the primary diagnosis if we just called this sarcoma."
