Abstract
Background: Idiopathic granulomatous mastitis (IGM) is a rare, benign, chronic inflammatory breast condition that poses diagnostic and therapeutic challenges. While corticosteroids are standard first-line therapy, some patients require additional immunomodulation, such as methotrexate. Predictive factors for step-up therapy remain poorly characterized. This study aimed to identify clinical, imaging, and pathological factors predictive of step-up therapy in IGM and evaluate associations between treatment approach and outcomes. Methods: A retrospective cohort study of women diagnosed with IGM was conducted between May 2022 and June 2024 at a tertiary center in Singapore. Data on demographics, clinical presentation, imaging, histopathology, and treatment were extracted. Step-up therapy was defined as methotrexate use following corticosteroids. Primary outcome was predictors of step-up therapy; secondary outcomes included treatment success, relapse, surgery, and time to remission. Statistical analyses included chi-square/Fisher's exact tests, Cox models, and Kaplan-Meier analysis. Results: Fifty-two women (median age 39 years) were included; 26 (50%) required step-up therapy. Predictors included oral contraceptive (OCP) use (RR 1.92; 95% CI 1.45-2.53; p < 0.001), smoking (RR 2.00; 95% CI 1.49-2.69; p < 0.001), flares (RR 2.33; 95% CI 1.44-3.79; p = 0.002), and percutaneous aspiration (RR 2.10; 95% CI 1.53-2.88; p = 0.025). Patients receiving methotrexate had lower relapse rates (RR 1.23; 95% CI 1.12-1.36; p < 0.001) but longer time to remission (adjusted HR 0.09; 95% CI 0.02-0.46; p = 0.004). Conclusions: OCP use, smoking, flares, and aspiration need may predict step-up therapy in IGM. Early identification could guide a more personalized, potentially top-down treatment.