Background

Recent studies suggest that antimalarials have antineoplastic properties.

Objective

To investigate whether antimalarials decrease the risk of cancer in systemic lupus erythematosus (SLE).

Methods

An observational prospective cohort study was carried out. 235 patients were included in the study at the time of diagnosis (American College of Rheumatology criteria). The end point was the diagnosis of cancer. Kaplan–Meier cancer‐free survival curves for patients treated and not treated with antimalarials were compared. A Cox proportional hazards model was fitted, with cancer as the dependent variable. Age at diagnosis, gender, treatment with azathioprine, cyclophosphamide and methotrexate, smoking, Systemic Lupus International Collaborating Clinics (SLICC) Damage Index 6 months after diagnosis, year of diagnosis and treatment with antimalarials were entered as independent variables.

Results

209 (89%) patients were women. 233 (99%) patients were white. Mean (SD) age at diagnosis was 37 (16) years. Median (range) follow‐up was 10 (1–31) years. 156 (66%) patients had ever received antimalarials. 2/156 (1.3%) ever‐treated patients compared with 11/79 (13%) never‐treated patients had cancer (p<0.001). Cumulative cancer‐free survival in treated and not treated patients was 0.98 and 0.73, respectively (p<0.001). Adjusted hazard ratio for cancer among malaria drug users compared with non‐users was 0.15 (95% CI 0.02 to 0.99).

Conclusions

This study launches the hypothesis of a protective action of antimalarials against cancer in patients with SLE. This effect should be confirmed in larger multicentre studies.