Radiation therapy (RT) directed at the primary tumor in men with metastatic castration-resistant prostate cancer (mCRPC) is safe and could improve survival, according to investigators.
Noaki Fujita, MD, of Hirosaki University Graduate School of Medicine in Hirosaki, Japan, and colleagues conducted a retrospective study of 105 men with mCRPC. The investigators divided the men into 2 groups: patients who received RT to the primary tumor after development of castration-resistant disease (31 patients) and those who did not receive RT (74 patients). Patients had a median age of 75 years at CRPC diagnosis. The median follow-up duration following CRPC diagnosis was 21 months. By the end of the follow-up period, 8 patients (26%) in the RT group and 48 (65%) in the no-RT group died from prostate cancer; 10 patients (32%) and 59 patients (80%), respectively, died from any cause.
Median cancer-specific survival (CSS) and overall survival (OS) times in the RT group were significantly longer than those in the no-RT group (66 vs 24 months and 66 vs 22 months, respectively), the investigators reported in Clinical Genitourinary Cancer. RT was significantly associated with 65% decreased risks for cancer-specific and overall mortality compared with no RT.
In subgroup analyses using the inverse probability of treatment weighting (IPTW) method, RT was significantly associated with improved OS in patients aged 75 years or older and those with initial PSA levels of 500 ng/mL or higher, cT4, Gleason score of 8 or higher, and high-volume metastatic burden compared with no RT.
RT was significantly associated with a 67% decreased risk of death among men aged 75 years or older; among men younger than 75 years, RT was not associated with survival.
Among men with an initial PSA level of 500 ng/mL or above, RT was significantly associated with a 74% decreased risk of death, but was not significantly associated with survival among men with lower initial PSA levels. RT was significantly associated with a 74% decreased risk of death among men with cT4 disease, but did not significantly improve survival among men with cT3 or less disease. RT was significantly associated with a 77% decreased risk of death among patients with Gleason score 8 or higher disease, but was not associated with survival among those with Gleason score 7 or less disease.
Among men with high-volume metastatic burden, RT was significantly associated with 69% decreased risk of death; among men with low-volume metastatic burden, RT did not significantly impact survival.
In the RT group, the rate of grade 3 or higher adverse events (AEs) was 23%, and the rate of any AEs was 55%, the investigators reported. The most common AE in any grade was anemia (26% of patients), followed by leukopenia (16%).
The investigators acknowledged study limitations, such as the relatively small number of enrolled patients. In addition, as the study was retrospective, they were unable to make definitive conclusions about the impact of RT on prognosis or control for selection bias and other unmeasured confounders.
Fujita N, Hatakeyama S, Momota M, et al. Safety and feasibility of radiation therapy to the primary tumor in patients with metastatic castration-resistant prostate cancer [published online March 13, 2020]. Clin Genitourin Cancer. doi: 10.1016/j.clgc.2020.03.009