Abstract
BACKGROUND: Recent cancer care advances have introduced new oral therapies, and yet population registries lack detailed treatment data, hampering investigations into therapy uptake, adherence, and outcomes. OBJECTIVE: This study aimed to assess the representativeness and completeness of linking Surveillance, Epidemiology, and End Results (SEER) cancer registry data with data from two major retail pharmacy chains, collectively covering a large segment of the US market. METHODS: A deterministic data linkage between 11 SEER cancer registries and retail pharmacy data (excluding mail order fills) was conducted for individuals diagnosed with selected cancers from 2013 to 2017, with follow-up through 2019. Descriptive characteristics of the linked and unlinked populations were examined. In a selected subcohort of older women (aged ≥65) with first and only primary breast cancer who had Medicare Part D claims for tamoxifen, we further validated the linkage using Medicare Part D event data as the reference standard. RESULTS: Among 758 068 eligible individuals, only 6.4% were linked to CVS/Walgreens data; the linkage percentage varied by age, sex, race, ethnicity, registry, and cancer type. Within the subcohort of 5963 older women with breast cancer and a claim for tamoxifen in Part D data, 25% were identified as tamoxifen users in retail pharmacy data. Out of these 1490 women, 749 (50.3%) had complete longitudinal tamoxifen dispensing information from retail pharmacy data. CONCLUSION: Retail pharmacy data show promise in identifying oral anticancer treatments, enhancing SEER registry efforts, but they require further validation. We propose an evaluation framework, sharing insights and potential use cases for this resource.