Answer: Diabetic mastopathy

Histology: This fragment of benign breast tissue is marked by dense, hyaline fibrosis, associated with plump epithelioid myofibroblasts. There is chronic inflammation, which is in a perivascular and perilobular distribution. Immunostains for cytokeratin highlight the normal grandular architecture of the breast tissue. This patient had a long history of diabetes, and thus the findings are consistent with diabetic mastopathy.

Discussion: The epithelioid myofibroblasts of diabetic mastopathy may mimic the invasive carcinoma cells of invasive lobular carcinoma. Immunohistochemistry for cytokeratin can make this distinction easily. Fibrocystic changes typically involve the lobules, and feature apocrine cysts. Low grade lymphoma would feature a more dense infiltrate of small lymphocytes which would infiltrate the benign breast tissue more.

The histologic findings of diabetic mastopathy are not completely specific, as they may be seen in other disorders such as thyroid diseases. However, in the appropriate clinical setting, the findings are typical of diabetes.