Use of methotrexate and risk of skin cancer: a nationwide case–control study

Background Methotrexate (MTX) use has been suspected of increasing the risk of skin cancer. The aim of this investigation was to examine the association between the use of MTX and the risk of basal cell carcinoma (BCC), cutaneous squamous cell carcinoma (cSCC) and cutaneous malignant melanoma (CMM). Methods In a nationwide Danish case–control study, we identified incident, histologically verified cases of BCC ( n = 131,447), cSCC ( n = 18,661) or CMM (26,068) from 2004 to 2018. We matched 10 controls to each case on sex and birth year using risk-set sampling and computed crude and adjusted odds ratios (ORs) using conditional logistic regression for the use of MTX (≥2.5 g) compared with never-use. Results Use of MTX was associated with increased risk of BCC, cSCC and CMM with adjusted ORs of (95% confidence interval) 1.29 (1.20–1.38), 1.61 (1.37–1.89) and 1.35 (1.13–1.61), respectively. For BCC and cSCC, ORs increased with higher cumulative doses. When restricting the study population to patients with psoriasis, the ORs were 1.43 (1.23–1.67), 1.18 (0.80–1.74) and 1.15 (0.77–1.72), respectively. Conclusions We observed an increased risk of BCC and cSCC associated with the use of MTX with evidence of a dose–response pattern; however, the association was not consistent when restricting the study population to patients with psoriasis.