#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 should be reported for a December 2013 diagnosis of lobular carcinoma in situ (8520/2) in the left breast, treated with a lumpectomy, followed by a July 2018 diagnosis of invasive ductal carcinoma (8500/3) also in the left breast? See Discussion.
In the April and July 2019 updates to the Solid Tumor Rules, the term simultaneous and Note 1 indicating histologies must be the same behavior were removed from rule M10 (ductal and lobular are a single primary).
We would like to confirm that rule M10 is the correct rule to apply to this case. This case is an invasive diagnosis approximately 4.5 years after an in situ diagnosis, so it seems like M17 should apply (invasive tumor following an in situ tumor more than 60 days later are multiple primaries).
An invasive tumor following an in situ tumor more than 60 days later of the same histology is a new primary. Similarly, it seems like an invasive tumor following an in situ tumor more than 60 days later of different histologies should be a new primary.
Abstract a single primary using 2018 Breast Solid Tumor Rule M10.
Unless the tumors were diagnosed more than 5 years apart, they are a single primary. The 2021 breast update will include examples and notes plus updating table 2.