#1: Solid Tumor Rules (2018)
#2: Multiple primaries
Source 1: 2018 Solid Tumor Rules
Notes: Breast, July 2019 Update
Solid Tumor Rules (2018)/Multiple primaries--Breast: How many primaries are there and how is histology coded for a breast primary showing encapsulated papillary carcinoma and Paget disease of the nipple? See Discussion.
Patient has a 1.7 cm encapsulated papillary carcinoma staged as pTis located 2 cm from the nipple and Paget disease of the nipple on mastectomy pathology.
There is no indication in Table 3: Specific Histologies, NOS/NST, and Subtypes/Variants that encapsulated papillary carcinoma is a subtype of ductal carcinoma. Rule M8 notes that if the histology of the underlying tumor is any histology OTHER THAN duct or subtypes of duct, one should continue through the rules. But if M9 applies to this case, then incidence reporting will be increased in comparison to prior years.
Abstract multiple primaries when there is Paget disease (8540/3) and an underlying tumor that is not duct, in this case, encapsulated papillary carcinoma (8504/2) using Rule M9 of the 2018 Breast Solid Tumor Rules.