Background: Granulomatous lobular mastitis (GLM) is a rare disorder that can clinically mimic breast carcinoma. The recommendation for diagnosis and treatment of GLM has not yet been established. 

Objectives: To assess a series of GLM patients, including their clinical presentation, diagnosis, treatment and outcome. 

Methods: We retrospectively analyzed the clinical data and treatment of 17 female patients with biopsy-proven GLM. Breast tissue was obtained by a core needle biopsy (15 patients) or open biopsy (2 patients). Images were reviewed by an experienced radiologist.

Results: The mean age of the patients at diagnosis was 44.6 ± 12.6 years. Five patients (29%) presented with bilateral disease, and seven (41%) presented with a mass, suggesting the initial diagnosis of breast carcinoma. Treatment comprised observation alone (23%), antibiotics (58.8%) and/or corticosteroids (with or without methotrexate) (35%). At the end of the study 70.6% of the patients demonstrated complete remission. None of the patients developed any systemic (granulomatous) disease or breast carcinoma during the follow-up period (4.7 ± 3.8 years). 

Conclusions: Core needle biopsy is mandatory for the diagnosis of GLM and the exclusion of breast carcinoma. The recommended treatment modalities are observation alone or corticosteroids; surgery should be avoided. GLM is a benign disease with a high rate of resolution and complete remission.