Associations of serum CA 15-3 with interstitial lung disease, PM/Scl100 antibodies and other disease characteristics in systemic sclerosis.

To investigate associations of serum CA 15-3 with interstitial lung disease (ILD), anti-PM/Scl100 antibodies, and other features in systemic sclerosis (SSc). 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. 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. 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.