Use of disease modifying anti-rheumatic drugs and risk of multiple myeloma in US Veterans with rheumatoid arthritis

Biologic (b) and targeted synthetic (ts) disease-modifying anti-rheumatic drugs (DMARDs) used in the management of rheumatoid arthritis (RA) target inflammatory pathways implicated in the pathogenesis of multiple myeloma (MM). It is unknown whether use of b/tsDMARDs affects the incidence of MM.

In this cohort study using Veterans Health Administration (VHA) data, we identified Veterans newly diagnosed with RA from 1/1/2002 to 12/31/2018 using diagnostic codes and medication fills. DMARD exposure was categorized as follows: conventional synthetic (cs)DMARDs; bDMARDs, which included tumor necrosis factor inhibitors (TNFi), non-TNFi; and a tsDMARD, tofacitinib. A Cox proportional hazards model with time-varying exposure was used to estimate the hazard ratio for developing MM among those who received b/tsDMARD medications relative to b/tsDMARD-naïve persons.

27,540 veterans with RA met eligibility criteria of whom 8322 (30%) took a b/tsDMARD during follow-up. There were 77 incident cases of MM over 192,000 person-years of follow-up. The age-adjusted incidence rate (IR) of MM among b/tsDMARD-naïve patients was 0.37 (95% CI 0.28–0.49) per 1000 person-years and 0.42 among current or former b/tsDMARD users (95% CI 0.25–0.65). Adjusting for age and other demographic characteristics, the hazard ratio for MM associated with use of b/tsDMARDs was 1.32 (95% CI 0.78, 2.26).

In this study of Veterans with RA, the rate of MM did not differ between b/tsDMARD and csDMARD users. The relatively short duration of follow-up and few events limited our power to detect treatment-related differences in MM risk.