e12557 Background: Biologic lateralization broadly impacts breast cancer. Malignancies originating in the left breast compared to the right breast tend to be more frequent, larger and of poorer prognosis. Left breast tumors respond differently to HER2-neu signaling and have lateralized Ki67 expression. In a prior study a right-left asymmetry in the neutrophil/lymphocyte ratio (NLR) of breast cancers was identified (ASCO 2018, e13094). As a follow-up, retrospective analysis of results from comprehensive genomic profiling (CGP) of right and left side breast cancer specimens was performed to determine a potential genomic etiology for the observed NLR lateralization. Methods: Tumors from 43 consecutive breast cancer patients underwent analysis for all classes of genomic alterations by hybrid capture-based CGP (Foundation Medicine). The CGP results from the 25 left- and 18 right-sided breast cancer samples were analyzed along with the histologic grade and status of estrogen receptor (ER), progesterone receptor (PR), and HER2 expression. Results: In this cohort of advanced breast cancer patients (stage 3-4), no statistically significant differences in lateralization were identified based on patient age, tumor stage, or frequency of ER or Her2 expression (Table). A predominance of PR positivity (p=0.14 chi square analysis) and amplifications in the ERBB2 (p=0.37) and RAD21 (p=0.08) genes were detected in right side tumors. Conclusions: Together with the prior study, trends in asymmetry based on genomic, pathologic, and immunohistologic differences have been detected in breast cancers, including an increased incidence of ERBB2 and RAD21 amplification in right-side breast tumors in this cohort. The predominance of lower PR positivity in the left breast tumors may be due to preferential hypermethylation, consistent with reports that it mediates biologic lateralization changes, downregulates PR expression, and alters amplification rates. Epigenetic methylation, may contribute to asymmetric breast cancer biology and have implications for therapeutic strategy. Further study is warranted.[Table: see text]
External-beam partial breast irradiation in a supine versus prone position after breast-conserving surgery for Chinese breast cancer patients
