Objective To investigate the risk of breast cancer recurrence in rheumatoid arthritis (RA)—patients with tumour necrosis factor inhibitor (TNFi) treatment and a history of breast cancer, taking several breast cancer, comorbidity and RA-related prognostic factors into account.

Methods 143 female TNFi-treated patients (1999–2010) with RA and a history of breast cancer before start of TNFi were identified through register linkages, and matched 1:1 from a cohort of 1598 comparable biologics-naive individuals. 120 TNFi-treated and 120 matched biologics-naive individuals with a history of equally recent/distant breast cancer met the eligibility criteria and comprised the final study population. The primary outcome was first recurrence of breast cancer. Through register-linkages and chart review, individuals were followed until 2011. HRs for recurrence were calculated using Cox regression.

Results The median time from breast cancer diagnosis until TNFi-treatment/start of follow-up was 9.4 years. Modest differences in breast cancer characteristics and/or treatment among TNFi-treated and biologics-naive individuals were noted at time of breast cancer diagnosis. Median follow-up from TNFi start was 4.9 years (4.6 years among biologics-naive). Among the TNFi-treated, 9 developed a breast cancer recurrence (crude incidence rate 15/1000 person-years) during follow-up, compared with 9 among the matched biologics-naive (16/1000 person-years). The adjusted corresponding HR was 1.1 (95% CI 0.4 to 2.8).

Conclusions Among patients with RA and a history of breast cancer, those who started TNFi-treatment did not experience more breast cancer recurrences than patients with RA treated otherwise. The generalisability of our findings to women with a very recent or a poor prognosis of breast cancer remains unknown.