Incidence of malignancy in idiopathic inflammatory myopathies

Summary: Abstract Body: Idiopathic inflammatory myopathies comprise a group of autoimmune conditions which can be paraneoplastic and which include both dermatomyositis (DM) and polymyositis (PM). DM is twice as common in women compared to men and is most closely associated with malignancy; as such, DM patients may undergo enhanced cancer screening as per recently published guidelines. However, PM may also be associated with increased risk of certain cancers, e.g. breast and colon cancer. In this study, we re-examine the associations of female DM and PM patients with cancer in a large US database (All of Us) which may reduce variations seen in smaller regional studies. We performed a matched, case-control study; female patients with a diagnosis of DM or PM up to 10 years before their enrollment in the All of Us study were included. We identified morphea controls with the nearest neighbor propensity score matching by age at condition diagnosis and race/ethnicity; morphea controls with comorbid systemic sclerosis or rheumatoid arthritis were excluded. To compare incidence of malignancy between groups, Kaplan-Meier curves were generated, and log-rank tests were performed. Malignancy was defined as hematologic and solid tumor malignancy for patients whose earliest diagnosis began after diagnosis of DM or PM. Within the All of Us dataset, we identified 168 patients with DM and 336 controls, and 140 patients with PM and 420 controls. Compared to controls, DM was associated with incidence of a malignant neoplastic disease within 1 year (5.49% vs 2.15%) and 5 years (17.5% vs 10.1%, p = 0.00923). PM was associated with incidence of a malignant neoplastic disease within 1 year (3.71% vs 2.19%) and 5 years (17.5% vs 9.31%, p = 0.0349). This study presents an association between incidence of malignancy and diagnosis of both DM and PM in US patients. Next steps include further elucidation of specific cancer types and timing of cancer onset with respect to onset of the DM/PM in this population, with the goal of further informing cancer screening approaches. Alina Feng¹, Anna Haemel² 1. School of Medicine, University of California San Francisco, San Francisco, CA, United States. 2. Department of Dermatology, University of California San Francisco, San Francisco, CA, United States. Adaptive and Auto-Immunity