Idiopathic granulomatous mastitis--a prospective study of 49 women and treatment outcomes with steroid therapy.

Idiopathic granulomatous mastitis (IGM) is an infrequently reported benign breast disease of unknown etiology. Surgical treatment has been widely advocated but can be disfiguring. We describe demographic and clinico-pathologic features of women with IGM in a safety net hospital, and evaluate steroid therapy as a breast-conserving modality of treatment. We also examine a possible ethnic predominance in Hispanic women. We conducted an observational prospective cohort study of all women with biopsy-proven granulomatous mastitis in the breast clinics of an urban safety net public hospital from 2006 to 2010. Demographic, ethnic and clinical data, treatment history, and response to treatment were collected. Patients were followed up prospectively to determine the type of treatment prescribed, complete resolution of disease, and median time to resolution. A nested case-control study was conducted to examine Hispanic prevalence using chi-square statistic. The mean age was 35 years. 80% were Hispanic. 80% presented with a painful breast mass. 59% initially received antibiotics with incomplete resolution. 90% women were prescribed oral steroids, 3% underwent surgical treatment, and 6% remained under observation with spontaneous resolution. Of those who received steroid, 80% had complete resolution of disease with a median time to complete resolution of 159 days (IQR 120-241 days). Ethnicity data in a nested case-control study revealed that women in the IGM group were more likely to be Hispanic than in the control group with an odds ratio of 3 (95% CI 1.42-6.24, p-value 0.0032). IGM is a benign but locally aggressive breast disease. Treatment with steroids is an effective breast-conserving option. Predominance in Hispanic women of childbearing age suggests a common genetic, environmental, immunologic, or infectious etiology and warrants further study with a multi-disciplinary approach.