ObjectiveBiologic disease modifying antirheumatic drugs (bDMARD) are immunosuppressants, and there have been concerns that they might impact tumor immunity in cancer patients with rheumatoid arthritis (RA). The purpose of this study was to describe the utilization trends of bDMARD in patients with RA after breast cancer (BC) diagnosis.MethodsWe performed a retrospective cohort study of adults with RA and BC (2008 onwards) from: Optum's de‐identified Clinformatics® Data Mart Database (CDM), the Surveillance, Epidemiology, and End Results Program (SEER)‐Medicare and the Texas Cancer Registry (TCR)‐Medicare databases. We evaluated bDMARD utilization trends during the first 3 years after BC. We conducted multivariable logistic regression to evaluate the association of utilization with patient characteristics.Results1,412 patients were identified in CDM and 1,439 patients in SEER/TCR‐Medicare. During the three months before BC diagnosis 28.2% (CDM) and 26.9% (SEER/TCR‐Medicare) patients had received bDMARD. Within the first three years after diagnosis 24.1% (CDM) and 26.4% (SEER/TCR‐Medicare) were receiving bDMARD. About 70% of the patients in the two cohorts received glucocorticoids with no significant time trend increases. The largest predictor of bDMARD use was prior use before BC: odds ratio (OR):27.15,95% confidence interval (CI):19.29‐38.19 (CDM), OR:18.98,95%CI:13.72‐26.26 (SEER/TCR). Distant and regional BC compared to in situ/localized were also associated with lower bDMARD in SEER/TCR‐Medicare (OR:0.54,95%CI:0.36‐0.82; OR:0.31,95%CI:0.13‐0.77).ConclusionThe use of tumor necrosis factor inhibitors (TNFi) and other bDMARD in patients with RA and recent BC has not increased since 2008. Glucocorticoids use remained high. Largest predictor of bDMARD utilization was prior use before BC.image