Capivasertib plus abiraterone in PTEN-deficient metastatic hormone-sensitive prostate cancer: CAPItello-281 phase III study.

[BACKGROUND] In metastatic hormone-sensitive prostate cancer (mHSPC), phosphatase and tensin homolog (PTEN) deficiency results in phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway activation, providing an independent proliferative drive, which cannot be suppressed by androgen receptor pathway inhibitors (ARPIs), resulting in worse outcomes. Dual inhibition of PI3K/AKT and AR pathways with capivasertib and abiraterone may delay progression and improve disease outcomes.

[PATIENTS AND METHODS] In CAPItello-281 (NCT04493853), patients with PTEN-deficient mHSPC (diagnostic cut-off: ≥90% viable malignant cells with no specific cytoplasmic PTEN immunohistochemistry staining) received capivasertib or placebo (1 : 1) plus abiraterone, prednisone/prednisolone, and androgen deprivation therapy (ADT). The primary endpoint was investigator-assessed radiographic progression-free survival (rPFS); overall survival (OS) was a key secondary endpoint. Post hoc exploratory subgroups at increasing PTEN cut-off thresholds were also assessed.

[RESULTS] 25.3% (1519/6003) of patients with valid tumor test results had PTEN-deficient tumors. In the randomized PTEN-deficient population, a statistically significant improvement in rPFS was observed with capivasertib plus abiraterone (n = 507, median 33.2 months) versus placebo plus abiraterone [n = 505, 25.7 months; hazard ratio (HR) 0.81, 95% confidence interval (CI) 0.66-0.98, P = 0.034]. Post hoc rPFS analyses for loss of PTEN cut-offs of ≥95%, ≥99%, and 100% showed that the capivasertib plus abiraterone arm performed consistently across cut-offs, but the placebo plus abiraterone arm performed progressively worse as the cut-off for the degree of PTEN loss was increased, resulting in a numerically improved treatment effect. In the overall population studied, the HR for OS (26.4% maturity) was 0.90, 95% CI 0.71-1.15, P = 0.401. The most common adverse events (AEs) for capivasertib plus abiraterone were diarrhea (51.9%; 8.0% placebo plus abiraterone), hyperglycemia (38.0%; 12.9%), and rash (35.4%; 7.0%). Deaths associated with an AE were reported in 36 (7.2%) and 26 (5.2%) patients in the capivasertib plus abiraterone and placebo plus abiraterone arms, respectively.

[CONCLUSIONS] Capivasertib plus abiraterone improves rPFS versus placebo plus abiraterone in PTEN-deficient mHSPC, on a background of ADT, with a 7.5-month improvement in median rPFS. AE profile was consistent with that of the individual agents. Patients with PTEN-deficient mHSPC benefit from dual blockade of the PI3K/AKT and AR pathways with capivasertib plus abiraterone.