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SEER Inquiry System - Report
Produced: 04/13/2026 9:40 AM
Question 20200070
Inquiry Details
References:
Solid Tumor Rules. Breast; December 2020 Update
Question:
Solid Tumor Rules (2018)/Multiple Primaries--Breast: The December 2020 revision to 2018 Breast Solid Tumor Rules, Rule M10, using behavior rather than timing to determine the number of primaries, has caused synchronous separate/non-contiguous tumors reported as invasive carcinoma, NST (8500/3) and lobular carcinoma in situ (8520/2) (or vice versa) to be reported as separate primaries per Rule M14. Should an invasive carcinoma NST and a synchronous, separate lobular carcinoma in situ be separate primaries per M14? See Discussion.
Discussion:
Recognizing the addition of the behavior requirement into this rule is an attempt to stop non-synchronous ductal carcinoma and lobular carcinomas from being accessioned as a single primary (SINQ 20200022), the issue with using behavior rather than timing is that now, synchronous separate/non-contiguous tumors that are invasive carcinoma NST (8500/3) and lobular carcinoma in situ (8520/2) (or vice versa) are separate primaries per M14.
Lobular and carcinoma, NST are separate rows in Table 3, so we cannot stop at M10 and code the mixed histology because there are two separate histologies with different behaviors. There is no rule that states we can just ignore the in situ tumors for the purpose of applying the M Rules. (We are instructed to ignore the in situ when coding histology only in certain circumstances.) The problem with Rule M10 appears to be related to timing.
This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.
Answer:
The original issue with M10 was with registrars being instructed that multiple in situ and invasive tumors were a single primary and then coding 8522/3 when one tumor was in situ and one was invasive. This incorrectly identified both components as being malignant (/3). Our effort to correct this misconception apparently did not work. M10 has been revised to state that yes, an in situ lobular or duct plus an invasive lobular or duct is a single primary with a new note that states: When a mixture of behaviors is present in carcinoma, NST, and lobular carcinoma, follow the H rules to determine the correct histology code. They will stop at H8 which instructs them to code the invasive histology. 8522/3 should only be used when both components are invasive.
