The Relationship Between Anti-Cell Division Cycle and Apoptosis Regulator 1 Autoantibodies, Anti-Sp4 Autoantibodies, and Cancer in Anti-Transcription Intermediary Factor 1γ-Positive Dermatomyositis.

Objective: The objective of this study was to describe the frequency, co-occurrence, and cancer association of anti-cell division cycle and apoptosis regulator 1 (anti-CCAR1) and anti-Sp4 in two large independent adult dermatomyositis (DM) cohorts.

Methods: Anti-transcription intermediary factor 1γ (anti-TIF1γ)-positive patients with DM from two independent cohorts were studied to determine the serologic overlap of anti-CCAR1 and anti-Sp4 autoantibodies measured by enzyme-linked immunosorbent assay. Associations between cancer-associated myositis (CAM) and antibody-defined subgroups within anti-TIF1γ-positive patients with DM were determined.

Results: A total of 305 anti-TIF1γ-positive patients with DM were studied: 169 patients from Johns Hopkins and 136 patients from Stanford. In each cohort, approximately one-third of anti-TIF1γ-positive patients with DM were anti-Sp4 positive, one-third were anti-CCAR1 positive, 20% were positive for both, and half of patients were negative for both. There was a strong association with CAM in patients lacking both these antibodies (Johns Hopkins, odds ratio [OR] 12.9 [95% confidence interval (CI) 3.6-89.5]; Stanford, OR 4.5 [95% CI 1.8-13.2]). The strongest negative association with CAM was found in patients with anti-Sp4 or anti-CCAR1 (Johns Hopkins, OR 0.07 [95% CI 0.01-0.27]; Stanford, OR 0.22 [95% CI 0.07-0.55]).

Conclusion: Both anti-Sp4 and anti-CCAR1 autoantibody subgroups are negatively associated with CAM. Although the magnitude of this association is substantial, cancer occasionally occurs in patients positive for either specificity. Conversely, approximately half of anti-TIF1γ-positive patients with DM are negative for both antibodies (anti-Sp4/anti-CCAR1 negative), and thus this subgroup may warrant more intensive cancer surveillance.