A 55-year-old woman was noted to have nodular breast masses on routine mammographic evaluation. A needle biopsy of one of the masses was performed. The resultant specimen is seen at several magnifications below.
The nodule consists of fibroinflammatory tissue with the inflammatory component being predominantly lymphocytic, with scattered plasma cells. There is a clear-cut lobular accentuation to the inflammation, but it also extends into the surrounding dense fibrous tissue.
What is your diagnosis?
Based on the histologic findings an inquiry was made with the referring pathologist regarding whether this patient was a diabetic. It was determined that the patient was indeed an insulin-dependent diabetic, and this is an excellent example of diabetic mastopathy.
This condition is thought to be an autoimmune response, possibly due to cross reacting antibodies developed to injected non-human insulin. Although often an incidental finding, it can occasionally produce painful nodules or multiple nodules detected on mammography but often not palpable. Patients are typically young to middle-aged women.
The fibrotic stroma is thought to be derived from activated myofibroblasts and these cells will often react, at least focally, for smooth muscle actin. Although not well seen in this more well-developed example, in "early" diabetic mastopathy, the proliferating myofibroblasts may have a distinctly epithelioid appearance leading to confusion with infiltrating carcinoma. If necessary a negative cytokeratin stain should alleviate that concern.
The lymphocytic infiltrate in this condition consists predominantly of B-cells, with only a scattered T-cell component. Histologically identical lesions may occasionally occur in women who are not diabetic. The terms "lymphocytic mastopathy" or "lymphocytic lobulitis" have been applied to these cases, although it seems likely that this is essentially the same process as in the diabetic patients.