Evaluation of biomarkers in multiple ipsilateral synchronous invasive breast carcinomas

Context.—The College of American Pathologists guidelines recommend testing additional tumor foci in multifocal invasive breast carcinomas for the biomarkers estrogen receptor (ER), progesterone receptor, and HER2 only if the carcinomas show different morphologies or grades. Objective.—To assess clinical significance of testing for biomarkers in additional tumor foci in multifocal invasive breast tumors. Design.—Retrospective analysis of 118 patients diagnosed with ipsilateral synchronous multifocal breast carcinomas from January 2015 through March 2016 at Mount Sinai Hospital (New York, New York). Results.—Eighty-six cases were tested for at least 1 of the 3 biomarkers in additional tumor foci. Fifteen cases (17%) showed discordant staining between the 2 foci for at least one biomarker. Of the 7 of 67 ER-discordant cases (10%), 4 (57%) showed major variation from negative to positive expression, including 3 cases in which a smaller tumor focus was strongly positive for ER whereas the index tumor was negative. Similarly, within the 7 of 67 progesterone receptor–discordant cases (10%), 4 (57%) showed major variation from negative to positive, and in 3 cases with major discordance, the index tumor was negative for progesterone receptor, whereas a smaller focus was positive. A difference in HER2 expression was noted in 5 of 86 cases (6%). In only 5 of the 15 patients (33%) with discordant results, biomarker testing on additional foci would have been offered per the College of American Pathologists recommendations because of differences in histology or grading. Of the remaining 10 patients, 7 (70%) with positive results on smaller foci would have been deprived of appropriate adjuvant systemic treatment if the smaller focus had not been tested. Conclusions.—We propose that negative values expressed in the primary tumor be repeated routinely on additional ipsilateral synchronous tumors.