Multifocal/Multicentric Ipsilateral Invasive Breast Carcinomas with Similar Histology: Is Multigene Testing of All Individual Foci Necessary?

Abstract

Multiple synchronous ipsilateral invasive breast carcinomas (BCs) with similar histology usually have concordant receptor status. It is unknown whether individual foci with similar histology also share molecular and biological similarities or are heterogenous. This study examined the concordance of the 21-gene recurrence score (RS) in multiple synchronous morphologically similar ipsilateral BCs. We identified patients with multiple ipsilateral BCs and available RS treated at our institution from 1/2014 to 6/2018. BCs were divided into three groups based on RS: (1) RS in same risk category, (2) RS in different risk categories but within 2-unit difference (e.g., RS 17 and RS 19), and (3) RS in different risk categories and a change of > 2 units. BCs in groups 1 and 2 were considered as concordant (no significant clinical impact) and BCs in group 3 as discordant (variation affects management). A total of 53 patients met the study criteria. RS was concordant in 46 (87%) cases. Seven (13%) cases were discordant (group 3). Of these, three (43%, 3/7) had biopsy cavity changes (BXC) adjacent to the BC with highest RS. In two cases the focus with higher RS had a lower percentage of progesterone receptor-positive tumor cells. In two cases, extensive ductal carcinoma in situ was associated with the BC focus with lower RS. Morphologically similar multifocal ipsilateral BCs have concordant RS in 87% (46/53) of cases. Our results suggest that, in cases of morphologically similar multifocal BCs, testing of a single focus provides accurate prognostic and predictive information.