Methylprednisolone for idiopathic granulomatous mastitis: a prospective observational cohort study

BACKGROUND: Idiopathic granulomatous mastitis (IGM) is a rare, benign, but locally aggressive breast disease. Steroids are widely used as a breast-conserving option, however, the response rate of steroids varies in reported studies, as well as its different reported usage. This prospective observational cohort study aimed to report the outcomes of methylprednisolone for IGM treatment. METHODS: From Aug 2019 to Dec 2021, the clinicopathological information of 156 IGM patients who sought treatment at West China Hospital was prospectively collected. A total of 88 patients treated with methylprednisolone were included in the study. The clinical features, treatment response, and follow-up data were analyzed. RESULTS: The median age at diagnosis was 32 years, and 90.9% of patients were multipara. The predominant symptom at presentation was painful breast mass, with a median size of 4.7 cm. For steroid usage, an initial 20 mg methylprednisolone daily was given until disease stable. The median duration of 20 mg methylprednisolone treatment was 45 (range, 14–376) days. The median duration of whole steroid therapy was 105 (range, 28–381) days. A total of 80.7% of patients (71/88) responded well to steroid treatment. In 63 patients, steroid treatment was successfully withdrawn, and treatment was completed. With an average of 283 days follow-up (range, 0–770 days), relapse was observed in 21 (33.33%) patients. Compared with patients with residual disease as shown by physical examination (PE), those with complete clinical remission (CCR) at the end of treatment had longer relapse-free intervals. CONCLUSIONS: Steroids are the preferable breast-conserving option for IGM. Treatment with 20 mg methylprednisolone for an average of 1.5 months is usually required, and full steroid treatment might last for 3 months.