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SEER Inquiry System - Report
Produced: 06/24/2026 1:26 PM
Question 20260004
Inquiry Details
References:
Solid Tumor Rules. 2026 Update, Breast
Question:
Solid Tumor Rules/Multiple Primaries--Breast: How many primaries and which Breast Solid Tumor Rules (STR) M Rule applies when a patient has synchronous, separate/non-contiguous breast tumors which are a ductal carcinoma and a separate lobular carcinoma? See Discussion.
Discussion:
Historically, synchronous ductal and lobular tumors have been accessioned as a single primary. These were previously covered under Rule M10, which was removed from the (STR) Manual 2026 Update. While the previous iteration of Rule M10 was problematic, the main issue related to the lack of a timing component within the rule (i.e., indicating it applied to synchronous ductal and lobular tumors).
Using the current Breast STR, when there are two (or more) simultaneous tumors which are not mixed lobular and ductal within each tumor, the applicable M Rule is Rule M13: Abstract multiple primaries when separate/non-contiguous tumors are on different rows in Table 3. To apply the M Rules, a provisional histology must be assigned to EACH tumor so we cannot code each tumor as 8522 before we start applying the M Rules. These provisional histologies would be 8500 and 8520, and these are on different rows in Table 3.
Answer:
Accession two primaries when a patient has synchronous, separate ductal and lobular tumors using Rule M13, Breast STRs, 2026 Update. Ductal carcinoma (8500/3) and lobular carcinoma (8520/3) are distinct histology terms and codes that are in different rows in Table 3. This is a modification of Rules M10 and H28 from prior versions of the STR Manual.
