BackgroundA higher incidence of apalutamide-related skin rash has been observed in Japanese patients with prostate cancer (PC).MethodsThis integrated analysis of data of Japanese patients from 2 global Phase 3 studies, SPARTAN (NCT01946204; patients with non-metastatic castration-resistant PC [nmCRPC]) and TITAN (NCT02489318; patients with metastatic castration-sensitive PC [mCSPC]), and the Phase 1 study 56021927PCR1008 (NCT02162836; patients with metastatic CRPC [mCRPC]), assessed clinical risk factors of apalutamide-related skin rash as well as the potential correlation with plasma exposure to apalutamide. Kaplan-Meier method was used for time-to-event analyses. Clinical risk factors for skin rash were assessed using odds ratio.ResultsData from 68 patients (SPARTAN: n = 34, TITAN: n = 28, 56021927PCR1008: n = 6) receiving apalutamide 240 mg orally once-daily were analyzed. Rash (13 [19.1%]) and maculo-papular rash (11 [16.2%]) were the most frequently reported skin rash. All Grade and Grade 3 skin rash occurred in 35 (51.5%) and 10 (14.7%) patients, respectively. Most (85.7%) skin rash occurred within 4 months of apalutamide initiation and resolved in a median time of 1 month following the use of antihistamines, topical or systemic corticosteroids, with/without apalutamide dose interruptions/reductions. Median time-to-remission of first incidence of rash and maximum grade incidence of rash were 1.0 month (IQR: 0.36–1.81) and 1.0 month (IQR: 0.30–2.43), respectively. No significant clinical risk factors for the incidence of skin rash were observed. Areas under the curve (0–24 h) (AUC0–24, ss) at steady-state of plasma apalutamide concentration were numerically slightly higher in patients with skin rash than those without.ConclusionsNo clinical risk factors for rash could be detected. There is a potential correlation between incidence of skin rash and plasma exposure to apalutamide. In general, apalutamide-related skin rash is easily managed, with appropriate treatment with or without dose adjustment.Trial registrationRetrospective pooled analysis of NCT01946204, NCT02489318, and NCT02162836.