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ObjectivesIn dermatomyositis (DM), autoantibodies are associated with unique clinical phenotypes. For example, anti-TIF1γ autoantibodies are associated with an increased risk of cancer. The purpose of this study was to discover novel DM autoantibodies.MethodsPhage ImmunoPrecipitation Sequencing using sera from 43 patients with DM suggested that transcription factor Sp4 is a novel autoantigen; this was confirmed by showing that patient sera immunoprecipitated full-length Sp4 protein. Sera from 371 Johns Hopkins patients with myositis (255 with DM, 28 with antisynthetase syndrome, 40 with immune-mediated necrotising myopathy, 29 with inclusion body myositis and 19 with polymyositis), 80 rheumatological disease controls (25 with Sjogren’s syndrome, 25 with systemic lupus erythematosus and 30 with rheumatoid arthritis (RA)) and 200 healthy comparators were screened for anti-SP4 autoantibodies by ELISA. A validation cohort of 46 anti-TIF1γ-positive patient sera from the University of Pittsburgh was also screened for anti-Sp4 autoantibodies.ResultsAnti-Sp4 autoantibodies were present in 27 (10.5%) patients with DM and 1 (3.3%) patient with RA but not in other clinical groups. In patients with DM, 96.3% of anti-Sp4 autoantibodies were detected in those with anti-TIF1γ autoantibodies. Among 26 TIF1γ-positive patients with anti-Sp4 autoantibodies, none (0%) had cancer. In contrast, among 35 TIF1γ-positive patients without anti-Sp4 autoantibodies, 5 (14%, p=0.04) had cancer. In the validation cohort, among 15 TIF1γ-positive patients with anti-Sp4 autoantibodies, 2 (13.3%) had cancer. By comparison, among 31 TIF1γ-positive patients without anti-Sp4 autoantibodies, 21 (67.7%, pConclusionsAnti-Sp4 autoantibodies appear to identify a subgroup of anti-TIF1γ-positive DM patients with lower cancer risk.

This study investigates cancer risk in idiopathic inflammatory myopathy (IIM) subgroups relative to the general population.We conducted a single center, retrospective cohort study of IIM patients and malignancy. Myositis-specific and -associated autoantibodies were determined by Euroimmun line blot, ELISA and immunoprecipitation. The Surveillance, Epidemiology, and End Results registry was used to compare the observed number of cancers to that expected in the general population, defined as a standardized prevalence ratio (SPR), adjusted for calendar year, age, sex, race, and ethnicity.1172 IIM patients, 203 (17%) with a cancer history, were studied. From cohort enrollment over a median follow-up of 5.2 years, the observed number of IIM patients diagnosed with cancer was increased 1.43-fold, SPR 1.43 (95%CI 1.15-1.77), p=0.002. Within 3 years of IIM-symptom onset, an increased SPR was observed for anti-TIF1γ-positive patients for ovarian and breast cancer (ovarian SPR 18.39 (95%CI 5.01-47.08), p0.001; breast SPR 3.84 (95%CI 1.99-6.71), p0.001). While anti-TIF1γ expectedly had a significantly elevated SPR, only 55% (36/66) of all cancers within 3 years of DM-onset were observed in TIF1γ-positive patients. Other MSAs including anti-Mi2, -SAE, and -NXP2 accounted for the majority of the remaining cancer diagnoses, 17/66 (26%), within 3 years of DM-onset. No cancer association, positive or negative, was observed for patients with anti-synthetase, anti-MDA5, or anti-HMGCR antibodies.In a tertiary referral center population, anti-TIF1γ was most strongly associated with breast and ovarian cancer. Patients with anti-synthetase, anti-MDA5, or anti-HMGCR antibodies had the same cancer risk as the general population. This article is protected by copyright. All rights reserved.