Serum Defensins in Differentiating Idiopathic Granulomatous Mastitis from Breast Cancer—Defensins in Idiopathic Granulomatous Mastitis and Breast Cancer

Background/Objectives: Differentiating idiopathic granulomatous mastitis (IGM) from breast cancer (BC) remains a significant clinical challenge due to overlapping clinical and radiological features. This study aimed to evaluate the diagnostic value of serum defensins and conventional tumor markers in distinguishing BC from IGM. Methods: A total of 150 participants were included: 50 with BC, 50 with IGM, and 50 with healthy controls. Serum levels of α-defensin 1, β-defensin 1, and β-defensin 2 were measured and compared across groups. In addition, inflammatory markers and tumor markers were analyzed. Receiver operating characteristic (ROC) analysis and logistic regression models were used to assess diagnostic performance. Results: Serum defensin levels were significantly higher in BC and IGM compared to healthy controls (p < 0.001), with β-defensin 2 showing the highest levels in BC. ROC analysis demonstrated high diagnostic accuracy for defensins (AUC: 0.95–0.99); however, in multivariable analysis, defensins were not retained as independent predictors, whereas CA15-3 and CA125 remained significant. The combined model based on CA15-3 and CA125 showed good discriminative performance (AUC = 0.83). Conclusions: Defensin levels, particularly β-defensin-2, were highest in BC and showed promising diagnostic potential; however, they should be considered adjunctive biomarkers. Their integration with conventional tumor markers and inflammatory parameters may improve differentiation between BC and IGM.