Abstract P1-18-18: PIK3CA mutation testing prevalence among post-menopausal (PM) women with hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer (mBC) using real world data
Authors: Princic Nicole , Said Qayyim , Smith David , Johnson William , Aizer Ayal 
Published: March 2020

Abstract
Background: Mutation testing has historically been of limited utility in patients with mBC due to the absence of approved treatments directed at specific genetic variants. However, the SOLAR-1 trial found improved progression-free survival with the addition of the PI3K inhibitor, alpelisib, to fulvestrant, versus placebo, among patients with PIK3CA mutated HR+/HER2- mBC, leading to FDA approval of alpelisib and indicating that PIK3CA mutation assessment has significant clinical relevance. The FDA approval for alpelisib after progression on endocrine therapy necessitates that PIK3CA status be ascertained relatively early in the course of disease of patients with HR+/HER2- mBC. We therefore examined the prevalence and timepoint of mutation testing encompassing PIK3CA among PM women with HR+/HER2- mBC in the United States (US).
Methods: This retrospective cohort study used administrative claims data from the MarketScan Commercial and Medicare Supplemental Databases, which include longitudinal records of medical services and prescription drugs from 25-30 million employees and dependents annually, covered by a variety of health plans. PM women diagnosed with mBC between 1/1/2012-7/31/2018 (index date = first metastasis diagnosis date) were selected. Patients were required to have HR+/HER2- disease defined by at least one prescription for endocrine therapy and no evidence of anti-HER2 targeted therapy post-index. The follow-up period was from index until inpatient death, disenrollment, or study end. Mutation testing was captured by a Current Procedural Terminology (CPT) code (81404, 81455, 81445) for polymerase chain reaction (PCR) or next generation sequencing (NGS) inclusive of PIK3CA mutation during the study period. The provider type on the BC-related outpatient physician office visit closest to the first mutation testing date was identified. Testing prevalence was calculated as percent of eligible PM women with HR+/HER2- mBC with a procedure code for PCR and/or NGS test.
Results: The study population included 8,499 mBC patients with mean (standard deviation [SD]) age 66.5 (10.6) years and an average follow-up duration of 1.9 (1.4) years. In total, 177 (2.1%) patients had NGS or PCR inclusive of the PIK3CA test during the study period. Of patients with a test, 28.8% (N=51) underwent testing prior to the start of first systemic therapy for metastatic disease (first line) and 126 (71.2%) were tested during or after first line (Table). Of patients with a test, 88.1% (N=156) had a BC-related outpatient physician office visit within 30 days prior to the test. The majority (55.1%) of visits (N=156) were with a hematologist-oncologist.
N%All eligible PM women with HR+/HER2- mBC8,499Patients with PCR and NGS testing inclusive of PIK3CA mutation177 2.1%Timing of earliest test (among those with testing) Prior to distant metastasis2212.4%From date of distant metastasis to first line2916.4%During first line4726.6%After first line7944.6%
Conclusions: Patients with HR+/HER2- mBC are infrequently tested for mutations such as PIK3CA, with majority of patients not being tested before the initiation of first line therapy. The demonstrated benefit of alpelisib in patients with PIK3CA mutations likely necessitates widespread testing for this important predictive factor early in the disease course. Future analyses are needed to determine the temporal trends over time and assess how genotype testing could be more standard.
Citation Format: Nicole Princic, Qayyim Said, David Smith, William Johnson, Ayal Aizer. PIK3CA mutation testing prevalence among post-menopausal (PM) women with hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer (mBC) using real world data [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-18.