Background/Purpose: Paraneoplastic myositis provide an exceptional opportunity for cancer triggered autoimmunity. Myositis specific antibodies (MSAs) show great clinical utility in IIM diagnosis and classification. However, cancer-associated MSAs has not been systematically identified, which may help for targeted cancer screening and provide clues to study cancer-immune system interactions. The objective of the study was to systematically evaluate the association between MSAs and cancer-associated myositis (CAM).

Methods: Sera from 627 idiopathic inflammatory myopathies (IIMs) patients were tested for MSAs. The cancer risk with different MSAs was estimated by standardized incidence ratio (SIR). The temporal relationship between myositis onset and cancer diagnoses, as well as the correlation between the clinical course of myositis and cancer in patients with IIM were evaluated.

Results: Compared with the general Chinese population, IIM patients with anti-TIF1-γ antibodies (SIR=17.28, 95% CI: 11.94 to 24.14); anti-NXP2 antibodies (SIR=8.14, 95% CI: 1.63 to 23.86); or anti-SAE1 antibodies (SIR=12.92, 95% CI: 3.23 to 32.94), or who were MSAs-negative (SIR=3.99, 95% CI: 1.96 to 7.14) faced an increased risk for cancer (Table 1). There was no association between specific MSAs subtypes and certain types of cancer. A close temporal relationship between the onset of myositis and cancer diagnoses was identified in the patients carrying anti-TIF1-γ, as well as other MSAs. In addition, a parallel between clinical course of myositis and cancer was observed in patients from various MSAs, such as anti-Jo-1 and anti-PL-12. There were no prognostic differences among the CAM patients from different MSA subgroups. However, patients with cancer developing within 1.5 year of myositis onset had a shorter survival time than those suffered from cancer beyond 1.5 year of myositis (17.0 vs. 45.0 months, p=0.004).

Conclusion: Our study demonstrates, in what is to our knowledge the largest population examined to date, that multiple myositis specific autoantibodies (anti-TIF1-γ, anti-NXP2, and anti-SAE1) are associated with cancer in IIM patients. Moreover, our data suggest that in some cases, anti-Jo-1 and anti-PL-12 antibody production might also be driven by malignancy. This can aid in the etiologic research of paraneoplastic myositis and clinical management.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-multiple-cancer-associated-myositis-specific-antibodies-in-idiopathic-inflammatory-myopathies-a-large-longitudinal-cohort-study/