BACKGROUND: A number of population-based epidemiological studies have been conducted to estimate the incidence rates of SPM (newly detected malignancies) among cancer survivors including those with prostate cancer. However, such data in patients with CRPC are limited. We conducted a retrospective cohort study of the SPM incidence among US men with CRPC.
OBJECTIVES: To explore the effect of varying the criteria for defining SPM and describe evidence for case confirmation in Medicare claims profiles.
METHODS: In the SEER-Medicare database, men aged >65 years with prostate cancer diagnosed in 2000-2011 were included if they had no other prior malignancy; had surgical or medical castration; and shad castration-resistant disease based on subsequent treatment with one of the following systemic therapies: abiraterone, cabazitaxel, docetaxel, enzalutamide, mitoxantrone, or sipuleucel-T. The base criteria for SPM (identified through 2013) were 1 inpatient claim, 2 outpatient claims, or 2 physician claims in Medicare data; or 1 diagnosis in SEER data. We reviewed Medicare claims profiles for cases of the 3 most common SPM identified by the base criteria. We also explored the effect of using a range of other case criteria.
RESULTS: The base criteria identified 172 SPM among the 2,234 men with CRPC, of which only 20 were in SEER data. The least restrictive criteria (a single claim in any Medicare file or a SEER diagnosis) identified 545 SPM. Claims profiles for the three most common SPM (lung/bronchus, n=29, 16.9%; urinary bladder, n=22, 12.8%; colon/rectum, n=21, 12.2%) identified by the base criteria had infrequent evidence specific enough to confirm a histologically distinct SPM (vs metastatic prostate cancer). Overall, SPM diagnoses were recorded a median of 3 times per patient in Medicare data. On average, SPM cases found in SEER had the diagnosis listed about twice as often in Medicare data as SPM cases not found in SEER (mean 11.8 vs. 6.0) (ratio, 2.0; 95% CI, 1.7-2.5) despite similar follow-up time.
CONCLUSIONS: Most SPM were identified only in Medicare data. We observed variability in SPM incidence rates depending on choice of criteria for their ascertainment.
