Cancer diagnosis in a Spanish cohort of multiple sclerosis patients under dimethylfumarate treatment

•New disease-modifying therapies are accompanied by safety concerns.•We describe multiple sclerosis (MS) patients who developed cancer while on dimethyl fumarate treatment.•A relationship between cancers and DMF was unlikely. The malignancy rate was similar to that of the population of the same age, sex and region.•Clinicians treating MS should be aware of any potential cancer symptom and demand proper testing.