April 2015 Case of the Month

42 year-old woman found to have a dense breast mass on mammography.  The patient then had a wire-localized excisional biopsy of the lesion, with the resulting histopathology below.  What is your diagnosis?

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Low power reveals areas of densely fibrotic stroma and interspersed adipocytes distributed within.

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Some areas of the lesion show vaguely keloid like appearance to the collagenous stroma.

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High power examination of these "epithelioid" cells show relatively bland nuclear cytology and abundant pale cytoplasm.

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Low power reveals areas of densely fibrotic stroma and interspersed adipocytes distributed within.

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April 2015 Case of the Month

   Answer: Lymphocytic Mastopathy/Diabetic Mastopathy

A limited panel of immunohistochemical stains were performed to characterize the epithelioid cells and rule out an epithelial neoplasm.  These cells were negative for CK AE1/AE3 and showed focal positivity for CD34 and desmin, thus supporting a myofibroblastic phenotype.  Given the morphologic features of this lesion, a phone call to the surgeon to elicit more clinical history revealed that the patient had type I diabetes mellitus.  Given that history and the triad of periglandular lymphocytes, keloid like collagenous fibrosis, and epithelioid myofibroblasts, this lesion is consistent with lymphocytic mastopathy/diabetic mastopathy.  Although not entirely clear, this lesion is thought to represent an autoimmune process.  Recurrences of these lesions have been reported.