The frequency of malignant neoplasms in patients with polymyositis-dermatomyositis. A controlled study.

Seventy-one patients with polymyositis-dermatomyositis (PM/DM) admitted to the Wellesley Hospital Rheumatic Disease Unit (RDU) in Toronto between 1965 and 1980 were followed up to 1981. The frequencies of malignant neoplasms occurring prior to or concurrent with initial RDU admission were compared, using case-control methods, with age- and sex-matched control groups with a diagnosis of any non-PM/DM rheumatic disease (rheumatic disease controls) or osteoarthritis, fibrositis, or fracture (noninflammatory musculoskeletal controls). In a cohort analysis, the incidence of malignant neoplasm subsequent to initial RDU admission in patients with PM/DM was compared with the expected incidence in the Canadian population. Fifteen of 71 patients with PM/DM had an antecedent or concurrent cancer compared with four of 71 rheumatic disease controls and one of 71 noninflammatory musculoskeletal controls. Cohort analysis showed no increase in the number of subsequent malignant neoplasms in patients with PM/DM compared with the age- and sex-matched Canadian population.