Granulomatous lobular mastitis (GLM) is a rare and chronic benign inflammatory disease of the breast. Difficulties exist in the management of GLM for many front-line surgeons and medical specialists who care for patients with inflammatory disorders of the breast. This consensus is summarized to establish evidence-based recommendations for the management of GLM. Literature was reviewed using PubMed from January 1, 1971 to July 31, 2020. Sixty-six international experienced multidisciplinary experts from 11 countries or regions were invited to review the evidence. Levels of evidence were determined using the American College of Physicians grading system, and recommendations were discussed until consensus. Experts discussed and concluded 30 recommendations on historical definitions, etiology and predisposing factors, diagnosis criteria, treatment, clinical stages, relapse and recurrence of GLM. GLM was recommended as a widely accepted definition. In addition, this consensus introduced a new clinical stages and management algorithm for GLM to provide individual treatment strategies. In conclusion, diagnosis of GLM depends on a combination of history, clinical manifestations, imaging examinations, laboratory examinations and pathology. The approach to treatment of GLM should be applied according to the different clinical stage of GLM. This evidence-based consensus would be valuable to assist front-line surgeons and medical specialists in the optimal management of GLM.

Background Idiopathic granulomatous mastitis (IGM) is a benign disorder of the breast, for which the optimal treatment modality remains missing. Methods A total of 124 patients with a histopathologically proven diagnosis of IGM were enrolled in a prospective, randomized parallel arm study. Patients were treated with topical steroids in Group T (n: 42), systemic steroids (0.8 mg/kg/day peroral) in Group S (n: 42), and combined steroids (0.4 mg/kg/day peroral + topical) in Group C (n: 40). Compliance with the therapy, response to the therapy, the duration of therapy, side effects and the recurrence rates were compared. Results Sixteen patients did not comply with the treatment, and the highest ratio of compliance with therapy was seen in Group T (p < 0.05). Complete clinical regression (CCR) was observed in 90 (83.3%) patients. Response to the treatment (RT) was evaluated radiologically and observed in 89.8% of the patients. There was no statistically significant difference between groups regarding CCR, RT and the recurrence rate. The longest duration of therapy was observed in Group T (22 ± 9.1‐week), whereas the shortest was observed in Group S (11.7 ± 5.5‐week) (p < 0.001). The systemic side effects were significantly lower in Group T in comparison with Groups S and C (2.4% vs. 38.2% and 30.3%, respectively) (p < 0.001). Conclusions The efficiency of the treatment was similar for all groups, both clinically and radiologically. Although the duration of therapy was longer in Group T, the lack of systemic side effects increased the compliance of the patients with the therapy. Therefore, topical steroids would be among first‐line treatment options of IGM.

Idiopathic granulomatous mastitis (IGM) rarely occurs with erythema nodosum (EN) as a systemic finding. However, the impact of their coexistence on disease severity and response to steroids has not been investigated yet. Patients diagnosed with IGM between September 2014 and October 2018 were divided into two groups according to the presence or absence of EN during the first admission retrospectively. The IGM was more severe in patients with EN as it was presented more often as bilateral and diffuse involvement of the breast. Findings of mastitis did not resolve with steroids in 50% of this group. Repetitive excisions and mastectomy with reconstructions were required to control the disease. Coexistence of EN and IGM was found to be related to bilateral and aggressive involvement, which could be associated with insufficient response to steroids. Associated patients should be informed in terms of the aggressive course, and surgery can be highlighted as a first-line treatment.