Abstract

Approximately 70% of all breast cancers are estrogen receptor positive (ER+BC) and endocrine therapy has improved survival for patients with ER+BC. Yet, up to half of these tumors recur within 20 years. Recurrent ER+BCs develop resistance to endocrine therapy; thus, novel targets are needed to treat recurrent ER+BC. We found that semaphorin 7A (SEMA7A) confers significantly decreased patient survival rates in ER+BC. We show that SEMA7A is hormonally regulated in ER+BC, but its expression does not uniformly decrease with anti-estrogen treatments. Additionally, overexpression of SEMA7A in ER+ cell lines drives increased in vitro growth in the presence of estrogen-deprivation, tamoxifen, and fulvestrant. In in vivo studies, we found that SEMA7A confers primary tumor resistance to fulvestrant and, importantly, induced lung metastases. Finally, we identify pro-survival signaling as a therapeutic vulnerability of ER+SEMA7A+ tumors and propose that targeting with inhibitors of survival signaling such as venetoclax may have efficacy for treating SEMA7A+ tumors. SIGNIFICANCEWe report that SEMA7A predicts for, and likely contributes to, poor response to standard-of-care therapies and suggest that patients with SEMA7A+ER+ tumors may benefit from alternative therapeutic strategies.