Serum CA 15-3 associations with interstitial lung disease, PM/Scl100 antibodies and other characteristics in systemic sclerosis: an exploratory cross-sectional study

Objectives: To investigate associations of serum CA 15 − 3 with interstitial lung disease (ILD), anti-PM/Scl100 antibodies, and other features in systemic sclerosis (SSc). Methods: We enrolled 59 SSc patients fulfilling 2013 ACR/EULAR criteria. CA 15 − 3 levels were compared between HRCT-confirmed ILD and non-ILD groups. Associations with autoantibodies, inflammation, patient-reported outcomes (PROs), and immunosuppressive therapy were assessed using nonparametric tests, ROC analysis, and multivariable logistic regression. Results: Patients with ILD (n = 23) had significantly higher CA 15 − 3 levels (median 29.8 vs. 18.6 U/mL, p = 0.007). ROC analysis yielded an AUC of 0.72 (95% CI 0.62–0.81, p = 0.002). CA 15 − 3 remained independently associated with ILD (OR 1.05 per U/mL, 95% CI 1.01–1.10, p = 0.021). CA 15 − 3 was also higher in anti-PM/Scl100–positive patients (34.5 vs. 21.0 U/mL, p = 0.01). No associations were seen with other disease features, CRP, ESR, IL-6, or PROs. Conclusions: Serum CA 15 − 3 is independently associated with ILD in SSc and elevated in anti-PM/Scl100–positive patients. It may serve as an accessible biomarker of pulmonary involvement, pending validation in larger cohorts.