IgG4-related sclerosing disease of the breast successfully treated by steroid therapy.

IgG4-related sclerosing disease was first identified and defined in the twenty-first century. In this pathology, the serum IgG4 level increases and IgG4-positive plasma cells and lymphocytes infiltrate organs such as the pancreas, salivary glands, lacrimal glands, kidneys, and the retroperitoneum. Presented in this report is a case of IgG4-related sclerosing disease that occurred in the breast and was treated successfully with steroid therapy. A 51-year-old woman presented with bilaterally swollen eyelids and an elevated serum IgG4 concentration. Screening CT revealed a lesion in her right breast but no other lesions. Mammography, ultrasonography, and MRI could not rule out malignancy, so a core needle biopsy was performed. Histologically, the lesion was composed of papilloma with fibrosis, adenosis, and severe lymphoplasmacytic infiltration. No malignant features were observed. Many plasma cells within the lesion were immunohistochemically positive for IgG4. IgG4-related sclerosing disease of the breast was diagnosed, and steroid therapy was initiated. During 4 weeks of steroid treatment the lesion became smaller in size, and at 7-months follow-up the lesion showed no new growth. Since steroid therapy is effective for this disease, IgG4-related sclerosing disease should be considered in the differential diagnosis of breast lesions in order to avoid unnecessary surgery.