Aims The aetiology and treatment options for idiopathic granulomatous mastitis (IGM) are controversial. The aim was to study the clinical and diagnostic features and discuss medical and surgical treatment for IGM in our patients.

Methods Sixty-five patients who met the histological criteria for IGM were retrospectively studied. The diagnosis of IGM was confirmed using Mammotome (an ultrasound-guided, vacuum-assisted biopsy system), core needle biopsy, quadrantectomy or segmental resection. Forty-five patients were treated with prednisolone (69.2%). Immunohistochemical (IHC) staining for immune-related antigens (CD3, CD4, CD8, CD79a, IgG, and IgM) was performed.

Results Ultrasonography (USG) was carried out in all patients. Among them, 61 were considered to have an inflammatory mass and 15 had accompanying liquefaction. In four patients, the findings mimicked breast carcinoma (6.2%). The IHC results showed CD3, CD4, CD8 and CD79a lymphocytes diffusely distributed in the lesion. Stains for IgG and IgM were negative. Prednisolone was administered to the patients diagnosed with IGM. The success rate was 53 (81.5%) and the whole recurrence was 12 (18.5%). The median follow-up period was 12 months (range 4–42 months).

Conclusions The aetiology of IGM remains uncertain. The disease has no propensity for the right or left breast. It is a local autoimmune disease, involving humoral and cell-mediated immunity. Hyperprolactinaemia may play a role in some patients. Corticosteroids administered after complete removal of the IGM lesion using the Mammotome biopsy system is an effective treatment option.