Incidence of Skeletal-Related Events in Patients with Castration-Resistant Prostate Cancer: An Observational Retrospective Cohort Study in the US

BACKGROUND AND OBJECTIVE: Skeletal-related events (SREs) are common in men with bone metastases and have negative consequences for patients with castration-resistant prostate cancer (CRPC), including pain, reduced quality of life, and increased mortality. We estimated incidence rates of first SREs in a cohort of men with CRPC in the Surveillance, Epidemiology, and End Results-Medicare database. METHODS: We included men aged ≥ 65 years with a prostate cancer diagnosis in 2000-2011 if they had no prior malignancy (other than nonmelanoma skin cancer) and had surgical or medical castration with subsequent second-line systemic therapy, which was used to infer castration resistance. The first occurrence of an SRE (fracture, bone surgery, radiation therapy, or spinal cord compression) in Medicare claims was identified. Incidence rates of SREs were estimated in all eligible person-time and, in secondary analyses, stratified by any use of bone-targeted agents (BTAs) and history of SRE. RESULTS: Of 2,234 men with CRPC (84% white, mean age = 76.6 years), 896 (40%) had an SRE during follow-up, with 74% occurring within a year after cohort entry. Overall, the incidence rate of SREs was 3.78 (95% CI, 3.53-4.03) per 100 person-months. The incidence rate of SREs before any BTA use was 4.16 (95% CI, 3.71-4.65) per 100 person-months, and after any BTA use was 3.60 (95% CI, 3.32-3.91) per 100 person-months. The incidence rate in patients with no history of SRE was 3.33 (95% CI 3.01-3.68) per 100 person-months, and in patients who had such a history, it was 4.20 (95% CI 3.84-4.58) per 100 person-months. CONCLUSIONS: In this large cohort of elderly men with CRPC in the US, SREs were common. A decrease in incidence of SREs after starting BTA is suggested, but the magnitude of the effect may be confounded by indication and other factors such as age and prior SRE.