BACKGROUND: A number of population-based epidemiological studies have been conducted to estimate incidence rates of SPM (newly detected malignancies) among cancer survivors, including those with prostate cancer. However, such data in patients with CRPC are limited. This study was conducted to estimate the incidence of SPM and overall survival (OS) in men with CRPC in the US.
METHODS: In the SEER-Medicare database, men aged > 65 years with prostate cancer diagnosed in 2000 through 2011 were eligible for the study if they had no other prior malignancy, had surgical or medical castration, and met the protocol-defined criteria for ascertaining castration resistance based on subsequent treatment with any of these therapies: abiraterone, cabazitaxel, docetaxel, enzalutamide, mitoxantrone, or sipuleucel-T. First SPM were identified in Medicare data as 1 inpatient claim, 2 outpatient claims, or 2 physician claims; or in SEER data as 1 diagnosis. Follow-up data ended in 2013. We estimated incidence of SPM as events per 100 person-years (py) with 95% confidence intervals (CI) and survival by the Kaplan-Meier method.
RESULTS: Among 2,234 men with CRPC (83.6% white; mean age, 76.6 years; 80.4% with bone metastases), we identified 172 with SPM, of which 20 (11.6%) were in SEER data. The incidence of all first SPM was 5.9 per 100 py (95% CI, 5.0-6.8). The most common of these were lung (n = 29), bladder (n = 22), colorectal (n = 21), other genitourinary cancers (n = 18), and non-colorectal gastrointestinal cancers (n = 17). Mean (SD) time from CRPC ascertainment to SPM was 1.0 (1.1) year. Median OS for the entire study population was 1.2 years (95% CI, 1.1-1.3) after CRPC ascertainment; estimated survival probabilities (95% CI) at 1, 3, and 5 years were 56% (54%-58%), 17% (15%-18%), and 9% (7%-11%), respectively.
CONCLUSIONS: Most CRPC patients had claims for a diagnosis of bone metastasis when CRPC was ascertained. SPM were common among the study population and occurred relatively soon after CRPC. Most SPM were identified in Medicare rather than SEER data. These results provided context for the incidence of SPM in men with CRPC up to 2013.
