Malignancy Risk and Predictors in Dermatomyositis and Polymyositis: A Large Population-Based Study

Area of Science:

• Rheumatology and Oncology
• Autoimmune Diseases and Cancer Epidemiology

Background:

• Idiopathic inflammatory myopathies (IIMs) are rare autoimmune disorders with known associations with malignancy, especially in dermatomyositis (DM).
• Previous studies on malignancy predictors in IIMs are limited by small sample sizes and lack of population-based data.
• Understanding site-specific cancer patterns and risk factors in large, diverse IIM cohorts is crucial.

Purpose of the Study:

• To evaluate malignancy patterns and identify predictors in a large, diverse cohort of patients with DM and polymyositis (PM).
• To assess the association between IIM subtypes and the risk of both solid and hematologic malignancies.
• To determine specific autoantibodies and clinical factors associated with increased cancer risk in IIM patients.

Main Methods:

• Retrospective cohort study utilizing the Clalit Health Services electronic database (2002-2018).
• Inclusion of 1557 DM patients and 528 PM patients, matched with controls at a 1:5 ratio.
• Analysis of malignancy incidence and risk using Cox proportional hazards models and logistic regression for predictors.

Main Results:

• DM showed a significantly increased risk for both solid and hematologic malignancies (HR 1.89), while PM had a less pronounced association limited to solid cancers (HR 1.50).
• In DM, elevated risks were observed for breast cancer (HR 1.86) and chronic leukemia (HR 5.02).
• Older age at diagnosis and specific autoantibodies (antiphospholipid, lupus anticoagulant, anti-Mi2, various antinuclear antibodies) were associated with increased malignancy risk across both subtypes.

Conclusions:

• Both DM and PM are associated with an increased risk of malignancy, with DM exhibiting a broader association including hematologic cancers.
• Older age and a distinct serological profile, particularly antiphospholipid and antinuclear antibodies, are key predictors of heightened malignancy risk.
• Heightened clinical vigilance is warranted for IIM patients with these risk factors to facilitate early cancer detection.