Rheumatoid arthritis, anti-tumour necrosis factor treatment, and risk of squamous cell and basal cell skin cancer: cohort study based on nationwide prospectively recorded data from Sweden

OBJECTIVE To investigate the risk of squamous cell and basal cell skin cancer in patients with rheumatoid arthritis naive to biologic drugs, in patients starting tumour necrosis factor (TNF) inhibitor treatment, and in the general population. DESIGN Population based cohort study. SETTING Nationwide data from Sweden. PARTICIPANTS Cohort of patients with rheumatoid arthritis naive to biologics (n=46 409), cohort of patients with rheumatoid arthritis starting TNF inhibitor treatment as first biologic in 1998-2012 (n=12 558), and matched general population comparator cohort, identified through national quality of care and health registers. MAIN OUTCOME MEASURE Hazard ratio of first in situ or invasive squamous cell skin cancer (1998-2012) and first basal cell cancer (2004-12). RESULTS For basal cell cancer, the hazard ratio was 1.22 (95% confidence interval 1.07 to 1.41) comparing biologics-naive rheumatoid arthritis patients with the general population and 1.14 (0.98 to 1.33; 236 v 1587 events) comparing TNF inhibitor treated patients with biologics-naive patients. For squamous cell cancer, the hazard ratio was 1.88 (1.74 to 2.03) comparing biologics-naive rheumatoid arthritis patients with the general population and 1.30 (1.10 to 1.55; 191 v 847 events) comparing TNF inhibitors with biologics-naive patients; the latter translated to an annual number needed to harm in the order of 1600. Among people with a history of squamous cell or basal cell cancer, TNF inhibitors did not further increase risks. CONCLUSION A small to moderately increased risk of basal cell cancer was seen in biologics-naive rheumatoid arthritis patients, with no further effect of TNF inhibitors. For squamous cell cancer, the risk was nearly doubled in biologics-naive patients, with a further 30% increase in risk among patients treated with TNF inhibitors; this translates to one additional case for every 1600 years of treatment experience, assuming that this association reflected causality. Vigilance regarding skin malignancies may be advisable in rheumatoid arthritis, irrespective of TNF inhibitor treatment. Most of the increase in risk for non-melanoma skin cancer in patients with rheumatoid arthritis treated with TNF inhibitors originates from factors other than that treatment.