Background: Biologic therapies used in the management of rheumatoid arthritis (RA) target several cytokines that have been implicated in the pathogenesis of multiple myeloma (MM). Yet little is known about the association between use of biologic or targeted synthetic disease modifying anti-rheumatic drugs (b or tsDMARDs) in RA and the incidence of MM.

Objectives: Our objective was to estimate the association between b/tsDMARD use and the risk of MM among persons with RA using Veterans Health Administration (VHA) data. We hypothesized that b-/tsDMARD use is associated with a lower incidence of MM compared with conventional synthetic DMARDs (csDMARDs).

Methods: In this retrospective cohort study, we identified patients >18 years of age diagnosed with RA in any United States VHA facility from 1/1/2002 and 12/31/2018. All patients met the following inclusion criteria: 1) two or more International Classification of Diseases Version 9 or 10 (ICD9 or ICD10) codes for RA at least 7 days apart but no more than 365 days apart 2) a prescription for a csDMARD within 90 days of the first RA diagnosis 3) one inpatient or outpatient visit 30 days to 2 years preceding first RA diagnosis (indicating a regular user of VHA). Medication data was derived from the outpatient prescription fills, bar coded medication administration (BCMA), and intravenous (IV) data domains. The csDMARDs included in these analyses were: methotrexate, sulfasalazine, leflunomide, and hydroxychloroquine. The bDMARDs included were tumor necrosis factor inhibitors (TNFi) and non-TNFi biologics such as tocilizumab, rituximab, abatacept, and biosimilars; tsDMARD was tofacitinib. Patients with MM before the diagnosis of RA were excluded. Incident MM was determined by 1 or more ICD9/10 code or ICD-oncology codes. Multivariable Cox proportional hazards model were performed to estimate the hazard ratio for developing MM among those during and following the use of a b-/tsDMARD relative to b-/tsDMARD-naïve persons adjusting for age, gender, race, and ethnicity.

Results: 27,540 veterans with RA met study eligibility criteria, of whom 8,322 (30%) had taken a b-/tsDMARD. Over the study period there were 77 incident MM over a total of 192,000 person years. There were 55 events in users of csDMARDs, an incidence rate (IR) of 0.40 (95% CI 0.30-0.52) per 1000 person-years and 22 in persons currently or formerly using b-/tsDMARDs (IR 0.41, 0.25-0.61 per 1000 person years). The unadjusted hazard ratio for MM following bDMARD use relative to csDMARD only use was 1.04 (0.63, 1.73), which increased to 1.28 (0.76, 2.16) after adjusting for demographic characteristics ( Table 1 ).

Conclusion: In this nationwide VA study, we did not observe an association between bDMARD use and the incidence of MM. Of note, the median interval from initiation of a bDMARD to the end of follow-up was approximately 5.8 years, which does not allow for an examination of a possible longer term influence.

Disclosure of Interests: None declared