The effect of reduced dose of apalutamide on skin adverse events in advanced prostate cancer: A multicenter retrospective study.

151 Background: We aimed to evaluate the effect of a reduced dose of apalutamide on skin-related adverse events (AEs) and castration-sensitive prostate cancer (CRPC)-free survival in patients with advanced prostate cancer. Methods: We retrospectively evaluated 35 patients with non-metastatic CRPC and 72 treatment naïve metastatic castration-sensitive prostate cancer (mCSPC) who were treated with apalutamide. The primary outcome was the effect of apalutamide dose-reduction on skin AEs. The secondary outcomes included the effect of apalutamide dose-reduction on skin AE in patents with small body size, post-skin AEs discontinuation rate, and the effect of apalutamide dose-reduction on CRPC-free survival in patients with mCSPC treated with upfront apalutamide plus androgen deprivation therapy. Results: Of 107 patients, 65 (60.7%) and 42 (39.3%) patients were treated with full- and reduced-dose of apalutamide, respectively. The skin AEs rate was not significantly different between the groups (55% vs. 43%, P = 0.761). The incident of skin AEs in the reduced dose of apalutamide were significantly lower in patients with small body size (body weight <67kg and body mass index < 24kg/m2) than those in other body sizes. Apalutamide discontinuation rate after skin AEs was significantly different between the full-dose (50%) and reduced-dose (16.7%) groups. Of 72 patients with mCSPC, the CRPC-free survival was not significantly different between the full- and reduced-dose groups. Conclusions: A reduced dose of apalutamide was not significantly associated with the incident of skin AEs. However, dose reduction for patients with small body size may decrease skin AEs without sacrificing oncological outcome.