IgG4-related disease of the breast: a systemic disease whose mammary manifestations mimic breast cancer

IgG4-related disease is a newly identified disease entity that has begun to attract attention, and international consensus diagnostic criteria for the condition have recently been proposed. The characteristic features of IgG4-related disease are lymphoplasmacytic infiltration involving a high proportion of IgG4-positive cells, fibrosis exhibiting a storiform pattern, and obliterative phlebitis. It can affect various organs, including the breast (in rare cases). IgG4-related disease has previously been referred to as inflammatory myofibroblastic tumor, plasma cell granuloma, or pseudolymphoma. We have experienced a case of IgG-related disease of the breast. Clinically and cytologically, the lesion was somewhat similar to a malignant tumor. An immunohistochemical examination of a core needle biopsy sample resulted in a correct diagnosis. In addition, a review of the patient’s clinical history revealed that the disease had affected areas other than the breast. Clinicians should be aware that breast lesions can be a focal manifestation of systemic disease, and overdiagnosis should be avoided by performing appropriate pathological analysis.