Low-dose methotrexate (LD-MTX), a cornerstone in the treatment of rheumatoid arthritis, is associated with a moderately increased risk of anemia, leukopenia, and skin cancers, but the risks of myelosuppression and malignancy during LD-MTX use remain incompletely described. We examined the risks of cytopenias and skin cancers among patients taking LD-MTX versus placebo in a large randomized controlled trial (RCT).
We prespecified secondary analyses of a double-blind, placebo-controlled RCT that included adults with known cardiovascular disease and diabetes or metabolic syndrome in the United States and Canada. Subjects were randomly allocated to LD-MTX (20 mg/week maximum) or placebo. All subjects received folic acid (1 mg daily for 6days/week). We assessed the frequency of blindly adjudicated hematologic and malignant adverse events (AEs).
A total of 2391 subjects were randomized to LD-MTX (mean dosage 14.9 mg/week), and 2395 were randomized to placebo. During follow-up, in the LD-MTX arm, simultaneous two-line cytopenias (n = 92 [3.9%]) or pancytopenia (n = 13 [0.54%]) were infrequent. Pancytopenia developed as soon as 4 months and as late as 3.5 years after beginning LD-MTX, though the latter subject had been recently diagnosed with multiple myeloma. Overall skin cancer risk was increased in users of LD-MTX compared with users of placebo, which driven largely by a statistically significant increased risk of squamous cell skin cancer (hazard ratio [HR] 3.31; 95% confidence interval [CI] 1.63-6.71). Melanoma was increased in LD-MTX, but this was not statistically significant (HR 2.33; 95% CI 0.60-9.01).
Among subjects using LD-MTX, simultaneous two-line cytopenias and pancytopenia were uncommon. We found more cases of skin cancer, particularly squamous cell carcinomas, in the LD-MTX arm than the placebo arm.

© 2020 The Authors. ACR Open Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.