Established and novel insights to guide cancer assessment in patients with idiopathic inflammatory myopathies.

Objective: Older age, dermatomyositis, and specific serum autoantibodies such as anti-TIF1-γ are associated with higher cancer risk in patients with myositis. We evaluated a vast cohort of patients with myositis for the prevalence of cancer, the association to disease features, and the performance of the recent IMACS guidelines.

Methods: A retrospective cohort analysis was performed and in all cases serum autoantibodies were tested using HEp-2, immunoassays, RNA- and protein-immunoprecipitation. Myositis was defined as cancer-associated if malignancy occurred within 3 years prior to or after the onset of myositis.

Results: Ninety-five patients with IIM were followed-up for a median of 6 years (interquartile range 3-11), the majority were classified as 'high-risk' or 'intermediate-risk' of cancer based on IMACS guidelines. A diagnosis of cancer was made in 22/95 (23 %) of cases and, based on the timing of the diagnosis, 14 % patients were cancer-associated myositis, with no significant differences compared to patients without cancer. Both groups of patients with overall cancer and cancer-associated myositis had more respiratory comorbidities, anemia, and hypergammaglobulinemia, and dermatomyositis phenotype. Anti-TIF1-γ antibody positivity predicted cancer-associated myositis but not the overall cancer rate; malignancy was observed in particular in patients with isolated anti-TIF1-γ antibodies, while a lower prevalence occurred in case of additional specificities identified by immunoprecipitation.

Conclusions: Recent IMACS guidelines perform well in the interception of cancer, yet adjunctive history and laboratory features should be considered. Patients with anti-TIF1-γ antibodies are at risk of cancer-associated myositis, but concurrent autoantibodies negatively correlate with malignancy and warrant characterization.