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Produced: 12/21/2025 3:48 PM
Question 20120082
Inquiry Details
References:
2007 MP/H Rules. M12
Question:
MP/H Rules/Multiple primaries--Breast: How many primaries are accessioned if the patient has two tumors in the left breast, one that is ductal carcinoma with mucinous differentiation and the other is ductal carcinoma, NOS? See Discussion.
Discussion:
The final diagnosis from the left mastectomy was multifocal invasive ductal carcinoma (mpT1cN0) with associated intermediate grade ductal carcinoma in situ located between the invasive foci.
Larger 2:00 focus: moderately differentiated ductal carcinoma with mucinous differentiation (1.4 cm).
Smaller 3:00 focus: moderately to poorly differentiated ductal carcinoma (1.2 cm).
The histologies of the invasive foci should be coded 8523/3 and 8500/3 respectively. To determine the number of primaries, does rule M11 apply which indicates this should be a single primary even though ductal with mucinous differentiation is not in Tables 1 or 2? Or does rule M12 apply because there is a difference in the third digit of histology and thus means this should be reported as a multiple primary case?
Answer:
For cases diagnosed 2007 or later, accession two primaries, ductal carcinoma with mucinous differentiation [8523/3] and ductal carcinoma, NOS [8500/3]. The steps used to arrive at this decision are:
Open the Multiple Primary and Histology Coding Rules Manual. Choose one of the three formats (i.e., flowchart, matrix or text). Go to the Breast MP rules because site specific rules have been developed for this primary.
Start at the MULTIPLE TUMORS module, rule M4. The rules are intended to be reviewed in consecutive order within a module. These tumors have ICD-O-3 histology codes that are different that the third (xxx) digit and are, therefore, multiple primaries.
Ductal carcinoma with mucinous differentiation is not a specific type of ductal carcinoma identified in either Table 1 or 2. (To locate Tables 1 and 2, go to Breast under the Terms & Definitions section of the manual.) It is ductal carcinoma mixed with another type of carcinoma (mucinous carcinoma in this case) see Table 3. Rule M11 does not apply.
