HER2 testing in breast cancers: comparison of assays and interpretation using ASCO/CAP 2013 and 2018 guidelines.

PURPOSE: HER2 overexpression and gene amplification are routinely tested by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), respectively. In addition, HER2 mRNA expression is also tested by the Oncotype DX assay. Discordance between laboratories among the different assays remains a problem. To improve the routine HER2 reporting, the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) updated their guidelines in 2018. Our study will compare concordance of HER2 status by IHC and FISH using ASCO/CAP 2013 and 2018 guidelines with Oncotype DX. METHODS: We retrospectively reviewed 657 estrogen receptor positive primary breast cancer cases with available Oncotype DX tests between 2011 and 2018. Medical records were reviewed for HER2 results by IHC, FISH, and Oncotype DX. The HER2 results by different assays and between 2013 and 2018 guidelines were compared. RESULTS: Of the 657 cases, 280 were tested by IHC, FISH, and Oncotype DX. HER2-equivocal cases by IHC 2013 guidelines were all negative (67/67, 100%) by FISH 2018 guidelines and by Oncotype DX. HER2-equivocal cases by FISH 2013 guidelines were all negative (16/16, 100%) by FISH 2018 guidelines, while 15/16 (93.8%) negative and 1/16 (6.2%) equivocal by Oncotype DX. The HER2-equivocal and HER2-negative groups were similar in age, gender, histology, grade, and Ki67 score. CONCLUSIONS: HER2 concordance was highest between Oncotype DX (99.6%) and FISH per 2018 guidelines. This suggests that the ASCO/CAP 2018 guidelines improved the accurate stratification of HER2-equivocal cases.

An Immunoscore Using PD-L1, CD68, and Tumor-infiltrating Lymphocytes (TILs) to Predict Response to Neoadjuvant Chemotherapy in Invasive Breast Cancer.

Response to neoadjuvant chemotherapy (NAC) in invasive breast cancer (IBC) is partly regulated by the immune microenvironment. We evaluated immune checkpoint PD-L1 expression, presence of CD68+ cells of macrophage/monocytic lineage and stromal tumor-infiltrating lymphocytes (TILs) in prechemotherapy biopsies and correlated with NAC response. We studied 76 cases of IBC. Prechemotherapy biopsies with >30% TILs were considered lymphocyte-rich IBC. We performed immunohistochemistry for PD-L1 and CD68. Prechemotherapy cores showing >1% PD-L1+ immune or tumor cells were considered positive. CD68 was positive if >40% of tumor stroma contained CD68+ cells or atleast 50% of tumor cells showed infiltration by CD68+ cells. Residual Cancer burden (RCB) Score of 0/I represented excellent response to NAC and RCB II or III unfavorable response. Thirty-five patients had RCB 0/I and 41 pts RCB II/ III. TILs>30% were present in prechemotherapy biopsies in 19 pts of whom 14 showed RCB 0/I (P=0.0075). Twenty-seven cases were PD-L1+ and 20 had an RCB 0/I (P=0.0003). Twenty-two cases were CD68+ of whom 18 showed RCB 0/I (P=<0.0001) There was a significant association between TILs>30%, PD-L1+ and CD68+ expression. Using atleast one of these immunologic parameters identified 26 of 35 patients with RCB 0/I and showed a higher sensitivity for response prediction than TILs alone (40% vs. 74.3%). In conclusion we demonstrate that high numbers of CD68+ monocytic/macrophage cells and PD-L1 expression in IBC shows significant association with NAC response. An immune biomarker profile including TILs, PD-LI and CD68 is more sensitive for NAC response prediction than TILs alone.