Malignancy is associated with dermatomyositis but not polymyositis in Northern New England, USA.

Objective: To retrospectively evaluate the association of idiopathic inflammatory myopathy (IIM) and malignancy in patients seen at 1 academic center over a 23-year period.

Methods: Patients were identified using the International Classification of Diseases, 9th edition (ICD-9) codes and diagnoses, then confirmed by chart review. Population cancer statistics obtained from the US Centers for Disease Control for Vermont and New Hampshire were used for comparison.

Results: Chart review confirmed IIM in 198 of 483 patients initially identified by ICD-9 codes. Within 5 years of diagnosis with IIM, malignancy developed in 32 patients (16.2%), 24 of whom (75%) had dermatomyositis (DM). Malignancy and DM developed within 1 year in 75%. The cancer risk associated with DM was much greater than the risk associated with other IIM. The most frequent tumor types were breast, lung, pancreas, and colon. DM patients with cancer were more frequently male and >or= 45 years of age than those without cancer. There were no cases of interstitial lung disease among patients with cancer and any form of IIM. The incidence of cancer was increased in patients with DM compared to age- and sex-matched population controls, both over a 5-year interval surrounding the diagnosis of DM and over the lifetime interval following diagnosis.

Conclusion: The risk of cancer in IIM is concentrated among patients with DM. The association between DM and cancer was enhanced by its temporal relationship (< 1 year) in 87.5% of these cases. Patients with malignancy-associated DM were more frequently male and over age 45 and less likely to have interstitial lung disease.