0166: Detection of the Novel Autoantibodies Against Transcription Factor Sp4 Is Related with Low Risk of Cancer in Idiopathic Inflammatory Myopathy Patients

Yuji Hosono¹, Azusa Kojima¹, Akira Ishii¹, Mai Sugiyama¹, Yuto Izumi¹, Noriko Sasaki², Chiho Yamada¹ and Shinji Sato¹, ¹Tokai University School of Medicine, Isehara Kanagawa, Japan, ²Tokai University School of Medicine, sagamihara-city, Japan

Background/Purpose: In idiopathic inflammatory myopathy (IIM), many kinds of autoantibodies are often detected and associated with each clinical phenotype. Recently, autoantibody against transcription factor Sp4 (anti-SP4) was newly discovered in IIM patient sera. However, whole clinical picture of anti-SP4 antibody-positive IIM is still unclear. Thus, the purpose of this study was to confirm the detection of anti-SP4 antibodies in IIM patients and investigate the clinical and serological features.

Methods: Adult Japanese IIM patients (N=201) who were treated at Tokai University hospital from 2012 to 2021 and healthy controls/non- systemic autoimmune rheumatic diseases (N=33) were enrolled. Anti-ARS, SRP Ab were screened by RNA-immunoprecipitation and anti-MDA5, Mi-2, HMGCR, Ku and TIF-1 Ab were detected by immunoprecipitation with [35S]methionine-labeled HeLa cells. Anti-SP4 was detected by immunoprecipitation and an enzyme-linked immune absorption assay. Clinical data was retrospectively collected.

Results: Among IIM patients,61% with antisynthetase syndrome, 17% with anti-MDA5, 13% with anti-TIF1γ,4% with anti-SRP, 2% with anti-Mi-2, 0.5% with anti-Ku, 0.5% with anti-HMGCR and 2.5% without any known autoantibodies. Anti-Sp4 autoantibodies was detected in 12.5% of DM and 1% of PM. Among DM patients, 55% (5/11) of anti-Sp4 autoantibodies were detected in patients with anti- anti-TIF1γ, 36% (4/11) were in anti-MDA5 and 18% (2/11) were in anti-Mi-2 autoantibodies. None of anti-SP4 autoantibody-positive DM patients had cancer. Among anti- anti-TIF1γ-positive DM patients, none of patients with coexisting anti-Sp4 had cancer, while 60% of those without anti-SP4 had (0% vs. 60%; p< 0.05, Chi-squared test).

Conclusion: In our study, anti-SP4 autoantibodies were frequency detected in PM/DM patients, and None of anti-SP4 autoantibody-positive DM patients had cancer. Coexisting of anti-SP4 autoantibodies may reduce the risk of malignancy in IIM patients, and screening for anti-SP4 autoantibodies is recommended at the diagnosis of IIM.

Disclosures: Y. Hosono, None; A. Kojima, None; A. Ishii, None; M. Sugiyama, None; Y. Izumi, None; N. Sasaki, None; C. Yamada, None; S. Sato, None.