Radium-223 for patients with metastatic castration-resistant prostate cancer with asymptomatic bone metastases progressing on first-line abiraterone acetate or enzalutamide: A single-arm phase II trial

Abstract

Purpose: The paper aims to evaluate the efficacy and safety of ²²³Ra in patients who progressed after first-line androgen deprivation therapy.

Patients and methods: EXCAAPE (NCT03002220) was a multicentre, single-arm, open-label, non-controlled phase IIa trial in 52 patients with metastatic castration-resistant prostate cancer and asymptomatic bone metastases who have progressed on abiraterone acetate or enzalutamide, up to six doses of ²²³Ra (55 kBq/kg of body weight per month). The primary end-point was radiographic progression-free survival (rPFS). Secondary end-points included rPFS based on androgen receptor splice variant 7 (AR-V7) expression in circulating tumour cells (CTCs), overall survival, and safety.

Results: Median rPFS was 5.5 months (95% CI 5.3-5.5). Median rPFS of patients with AR-V7(-) CTCs was longer than that of patients with AR-V7(+) CTCs (5.5 versus 2.2 months, respectively; P = 0.056). Median overall survival was 14.8 months (95% CI 11.2-not reached) and was significantly greater for AR-V7(-) patients than for AR-V7(+) patients (14.8 months versus 3.5 months, respectively; P < 0.01). ²²³Ra was well tolerated; anaemia and thrombocytopenia were the most common grade 3/4 adverse events (5.8% and 11.5%, respectively).

Conclusions: ²²³Ra seems to be a reasonable treatment for patients with metastatic castration-resistant prostate cancer and asymptomatic bone metastases progressing on novel hormonal therapy and had an acceptable safety profile.

Keywords: AR-V7; Bone metastases; Metastatic castration-resistant prostate cancer; Radium-223.