Comparison of estrogen receptor, progesterone receptor and HER2 results in concurrent ipsilateral samples with invasive breast carcinoma: a retrospective study of 246 biopsies from 119 patients.

There is no consensus regarding biomarker testing on the ipsilateral breast carcinomas present in separate biopsies, irrespective of whether the biopsies are performed concurrently or consecutively. We aimed to investigate estrogen receptor (ER), progesterone receptor (PR) and HER2 concordance in ipsilateral concurrent biopsies with invasive breast tumors. Consecutive ipsilateral concurrent biopsies with invasive breast tumors were identified retrospectively. Biomarker results, histologic grade and histologic subtype among the tumors in concurrent samples were compared. ER, PR, and HER2 expression was different in 3 (2.5%), 11 (9.2%) and 7 (5.9%) cases, respectively. All ER-discordant cases were sets of ER-negative (ER-) and weak-low ER-positive (ER+), ductal subtype and histologic grade 2 or 3 tumors. All PR-discordant cases were ER+, and comprised of histologic grades 1 to 3 ductal as well as lobular tumors. All HER2 discordant cases were histologic grade 2 to 3 ductal tumors. Biomarker discordance was independent of grade and subtype discordance. We found very low biomarker discordance among tumors in concurrent samples from ipsilateral breast. Our results suggest that ER and HER2 discordance in concurrent samples is predictable. ER discordance is present only in a setting of low ER+ tumors. Low-grade ductal and/or lobular tumors are ER and HER2 concordant. HER2 discordance is noted in grade 2 to 3 ductal tumors only. Histologic subtype and grade may guide extent of biomarker testing in concurrent ipsilateral breast biopsies.