No increase in cancer incidence detected after cyclophosphamide in a French cohort of patients with progressive multiple sclerosis

Background: Cyclophosphamide is still used in progressive forms of multiple sclerosis (MS) in view of its suggested efficacy and safety in the short term. No data exist on its long-term safety in MS, particularly on the risk of malignancy.Objective: The objective of this study was to evaluate cancer incidence in MS after cyclophosphamide treatment.Methods: We performed a historical prospective study in a cohort of MS patients treated with cyclophosphamide. We collected demographic data and medical history from medical databases and patient interviews. Reported cancers were histologically confirmed. Cancer incidence was compared with the incidence in the general population by estimating standardized incidence ratios (SIRs).Results: We included 354 patients, with a median follow-up of 5 years (range 2–15) after cyclophosphamide treatment. Fifteen patients developed a solid cancer, which occurred at a median of 3 years (range 0.5–14) after cyclophosphamide introduction. The cumulative incidence of cancer aft...