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SEER Inquiry System - Report
Produced: 05/24/2025 12:52 PM
Question 20200072
Inquiry Details
References:
Solid Tumor Rules. Breast; December 2020 Update
Question:
Solid Tumor Rules (2018)/Multiple Primaries--Breast: How many primaries are accessioned when there are multiple synchronous/non-contiguous tumors when one tumor is metaplastic carcinoma (with carcinoma No Special Type (NST) or lobular carcinoma) and another tumor is strictly carcinoma, NST? See Discussion.
Discussion:
Is an M rule needed to address multiple tumors and Note 2 in Table 3? Does Note 2 in Table 3 apply when multiple tumors exist and one tumor contains only ductal carcinoma?
The M Rules currently confirm that a metaplastic carcinoma (whether it is involved with ductal or lobular) and a separate ductal carcinoma are separate primaries because these histologies are on different rows in Table 3 (separate primaries per M14). There is no specific rule regarding metaplastic carcinomas in the Multiple Tumors (M Rules) module, so presumably, the presence of a separate ductal carcinoma is not lumped into Note 2 in Table 3 for metaplastic carcinoma.
However, the note is confusing when there are multiple tumors involved because it appears to the registrars there are two options for coding the histology. To some registrars, the rules indicate it does not matter if the tumor is predominantly ductal carcinoma as long as some percentage of metaplastic carcinoma is present, code histology to metaplastic carcinoma. For other registrars, the presence of solely a ductal carcinoma in a second tumor is a separate primary from the separate metaplastic carcinoma.
The M rules and Note 2 need to clarify this issue to promote consistency.
This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.
Answer:
The term "mixed" implies a single tumor comprised of metaplastic carcinoma or variants of metaplastic and duct or lobular. The metaplastic histology is coded regardless of whether it comprises the majority (greater than 50% of the tumor). M13 is the only rule specific to metaplastic and is in the single tumor module. This implies a single tumor with both histologies. When there are multiple tumors, one with metaplastic or a subtype/variant of metaplastic and another with a histology listed on a different row, continue to the Multiple Tumors module. M13 applies and there are two primaries. We will add "single tumor" to the note in Table 2 in the next update.
