Genomic testing and uptake of alteration-targeted therapies among patients with hormone-receptor positive (HR+) metastatic breast cancer (MBC).

e13084 Background: There is no recognized standard of care treatment after progression on first-line endocrine therapy plus CDK4/6 inhibitor in HR+ / HER2 negative MBC. Alteration-targeted therapies (ATT) have the potential to delay initiation of chemotherapy with more favorable toxicity, and perhaps improved efficacy. Next-generation sequencing (NGS) of tumor tissue or circulating tumor DNA (ctDNA) can identify actionable mutations for targeted therapy. In this study, we sought to assess the results of genomic testing and uptake of ATT among patients with HR+ / HER2-negative MBC. Methods: We studied a retrospective cohort of patients with MBC who received treatment in the Koontz Center for Advanced Breast Cancer (KABCC) at St. Luke’s Cancer Institute, a community-based health system in the Kansas City metro area. The analytic cohort included 125 patients with HR+ / HER2-negative MBC who received treatment after progression on first-line therapy. Genomic testing was performed as a standard of care from ctDNA or tumor-tissue using commercially available NGS assays. Targetable alterations were defined as those with FDA-approved or routinely used off-label treatment regimens in MBC ( PIK3CA, PTEN, AKT, ESR1, ERBB2, BRCA1, BRCA2, PALB2 mutations; TMB >10 or PDL1+). We identified patients who received any ATT and compared them with those who did not. Overall survival (OS) and time to initiation of chemotherapy (TTC) were compared between the two groups using Kaplan-Meier analyses and the log-rank test. Results: Ninety-nine patients (79.2%) had genomic testing and 49 (39.2%) were tested prior to second-line therapy. Of those tested, 84% had at least one targetable alteration. ESR1 mutations were most common, detected in 36% of patients, followed by PIK3CA (31.2%), PTEN (12%), BRCA1/2 (7.2%) and ERBB2 (5.6%). A total of 35 patients received ATT, and around half of those (17 patients) received ATT in the second line. Alpelisib was the most common ATT (62.9%), followed by elacestrant (20%) and neratinib (14.3%). There was no significant difference in OS or TTC between the two groups. Conclusions: Approximately 80% of patients with HR+ / HER2-negative MBC in our cohort underwent genomic testing after progression on first-line therapy, and the vast majority had at least one targetable alteration identified. However, only 35 patients received ATT with most receiving alpelisib. We observed no significant improvement in OS or TTC among those who received ATT, although the numbers were small. There have been two new targeted therapies approved in the past year and many novel agents are currently under investigation in clinical trials. Newer therapies with distinct targets, improved tolerability and efficacy have the potential to improve the uptake and clinical benefit of targeted therapy in MBC.