Adiposity and response to androgen signaling inhibition (ASI) in men with metastatic castration-resistant prostate cancer (mCRPC).

72 Background: Improved understanding of how host factors influence the efficacy and toxicity of ASI could improve outcomes. Adiposity increases the risk for recurrence and lethal disease in men with localized prostate cancer. Few studies have evaluated the influence of adiposity in metastatic prostate cancer, and in these studies, adiposity was associated with improved outcomes, a potential “obesity paradox”. Herein, we assess whether adiposity is associated with response to maximal ASI in mCRPC and assess how individual body composition measurements interact to influence outcomes. Methods: Men with mCRPC uniformly treated on a prospective clinical trial with abiraterone acetate plus apalutamide were included in this post-hoc analysis (NCT02703623). Responders were defined as those with a decrease in PSA of > 50% after 8 weeks of therapy. Body composition was assessed at the level of L3 on baseline CT scan at trial registration using Slice-O-Matic version 5.0. Body composition indices were normalized for height (m2). Non-parametric Kruskal-Wallis test was used to evaluate associations between continuous baseline measures. A multivariable CART model was used to determine if baseline measures could divide patients into distinct risk groups. Results: In 186 men with mCRPC, responders to maximal ASI (n = 128) had higher subcutaneous adiposity (SATi, 79.3 vs. 67.6, p = 0.02), visceral adiposity (VATi, 76.4 vs. 61.5, p = 0.03), and body mass index (BMI, 30.3 vs. 29.2, p = 0.04). There was a strong correlation between BMI and SAT (r = 0.81). In exploratory multivariable modeling, BMI and VATi had the strongest associations with response to ASI. Specifically, men with a BMI ≥ 26.73 had a higher response rate (75% vs. 46%). For men with a BMI < 26.73, a VATi ≥ 24.7 enriched for response to therapy (86% vs. 26%). Conclusions: Elevated subcutaneous and visceral adiposity is associated with improved response to maximal ASI in men with mCRPC. In hypothesis-generating models, visceral adiposity had the strongest association with response to ASI in men with lower BMI. Further studies need to assess how and when adiposity becomes favorable for outcomes in advanced prostate cancer.