Independent assessment of TP53 and PTEN as predictors of response to enzalutamide (ENZ) or abiraterone acetate (AA) in men with metastatic castration-resistant prostate cancer (mCRPC).

Abstract

351 Background: Alterations in androgen receptor signaling are well-established mechanisms of resistance to medical castration. Pre-clinical studies suggest that alterations to key tumor suppressor genes, such as TP53 or PTEN, may also be associated with development of androgen independence as an alternate mechanism of castration-resistance. Previous studies have shown that TP53 inactivation and PTEN loss are predictive of response to novel androgen axis inhibitors. Here, we independently assess whether TP53 and PTEN genomic alterations are predictive of response to ENZ and AA in men with mCRPC. Methods: Clinical data and samples were analyzed from a prospective prostate cancer registry at the University of Utah (Salt Lake City, UT). Next-generation sequencing (NGS) was performed on predominantly primary tumor tissue for 343 somatic and germline genetic alterations using FoundationOne. Primary endpoints were progression-free survival (PFS) and overall survival (OS). Patients with mCRPC who were treated with any line AA or enzalutamide were included. We performed a univariate analysis to assess the predictive value of TP53 and PTEN. Only patients treated with single-agent therapy were included. Results: Of 141 men with prostate cancer and NGS available, 56 were included. Most patients were treated with abiraterone (n = 50), and only 6 with enzalutamide. 28.6% had PTEN loss and 35.7% had a TP53 mutation. OS and PFS did not differ significantly according to PTEN or TP53 status. Median OS was 40.9 months and not reached for men with and without TP53 mutation (HR 1.85, p = 0.31). Median PFS was 7.5 months and 9.5 months for men with and without TP53 mutation (HR 1.18, p = 0.60). Median PFS was 7.2 months and 9.5 months for men with and without PTEN loss (HR 1.15, p = 0.66). Median OS for PTEN was not mature enough to analyze. Conclusions: In our independent cohort, neither TP53 mutation nor PTEN loss is predictive of response to androgen-directed therapy in men with mCRPC patients. However, this is a relatively small retrospective sample with few events. These results should be considered exploratory only.