Abstract 29: Utility of novel clinico-genomic data to understand patient characteristics, treatments, and outcomes according to <i>PIK3CA</i> mutation status among hormone receptor-positive metastatic breast cancer patients (2020)

Abstract Background: Hormone receptor-positive (HR+) breast cancer (BC) comprises 60-65% of all BC. Activating mutations in PIK3CA are the most common oncogenic alteration in HR+ BC, yet little is known about the prognostic utility of single (SM) and multiple (MM) PIK3CA mutations. A novel database with next-generation sequencing (NGS) data from Foundation Medicine, Inc. (FMI) linked to electronic health records-derived clinical data from Flatiron Health allows investigation of the prognostic utility of genomic alterations including PIK3CA. Using this database, this study seeks to understand HR+/human epidermal growth factor receptor 2-negative (HER2-) metastatic BC (mBC) patient (pt) testing behavior, characteristics, and survival according to PIK3CA mutation status. Methods: Pt-level data from US pts diagnosed with HR+/HER2- mBC from January 1, 2011 to December 31, 2018 were selected from the de-identified Flatiron Health-FMI Clinico-Genomic Database (CGDB). Kaplan-Meier methods were used to estimate median (95% confidence interval [CI]) survival time, defined as time from mBC diagnosis to death. Multivariable Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs. Index date was mBC diagnosis date, but adjustments were made in survival analyses to account for delayed dataset entry due to FMI results date occurring after mBC diagnosis date. Descriptive statistics and chi-square and Kruskal-Wallis tests for significance were used to compare pt characteristics. Results: Of 1349 HR+/HER2- mBC pts included in this study, 807 pts (60%) were wild-type (WT) for PIK3CA, 436 (32%) were SM, and 106 (8%) were MM. Only 2% of pts had an FMI results date before mBC diagnosis date. Most pts had an FMI results date either during (26%) or after (59%) first-line treatment. Median time from mBC diagnosis to FMI results date was longer for MM (19 mo) vs. SM (13 mo) and WT (13 mo) pts (p=0.15). SM and MM pts were older than WT pts at mBC diagnosis (median: 59.9 yr [MM] vs. 59.6 yr [SM] vs. 56.2 yr [WT], p&amp;lt;0.001) and more often had progesterone receptor (PR)-positive BC (88.6% [MM] vs. 86.5% [SM] vs. 74.6% [WT], p&amp;lt;0.001). Median survival times for WT, SM, and MM pts were 20, 23, and 30 mo, respectively (p=0.40). After adjusting for age, site of metastasis at mBC diagnosis, and estrogen receptor/PR status, there was no association with overall survival for MM vs. WT (HR=0.96, p=0.53) or SM vs. WT (HR=1.03, p=0.80). Conclusions: These data showed that PIK3CA mutations were not associated with survival in this patient population and underscore the utility of linked clinical and genomics data for understanding the relationship between genetic alterations and patient outcomes. The majority of HR+/HER2- mBC pts received FMI results more than a year after mBC diagnosis, suggesting that NGS testing is used to guide decisions after pts have failed standard therapy. Additional studies with larger sample sizes and longer follow-up are needed to confirm these observations. Citation Format: Mary K. Downer, Peter Lambert, Sami Mahrus, Katherine E. Hutchinson, Patricia Luhn, Jennifer L. Schutzman. Utility of novel clinico-genomic data to understand patient characteristics, treatments, and outcomes according to PIK3CA mutation status among hormone receptor-positive metastatic breast cancer patients [abstract]. In: Proceedings of the AACR Special Conference on Advancing Precision Medicine Drug Development: Incorporation of Real-World Data and Other Novel Strategies; Jan 9-12, 2020; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_1):Abstract nr 29.