Answer: Multiple micropapillomas

Histology: At low power, the breast contains multiple nodules with sclerosis. Higher power view of these nodules reveals areas of both hyalinized, sclerosis, and desmoplastic reaction. The underlying lesion is a papillary one characterized by fibrovascular cores, but these are distorted by sclerosis and desmoplasia. Cytologically, the epithelial proliferation within these sclerotic papillomas, while florid, is benign. The nuclei are, in general, overlapping, hypochromatic, and variable in size and shape. Spaces formed by the epithelial cells are slit-like. There are foci of necrosis, but this is acceptable in benign sclerosed papillary lesions.

Discussion: Papillary carcinoma would feature more hyperchromatic nuclei within more uniform epithelial cells surmounting the papillae. Myoepithelial cells may be absent. Papilloma typically occurs within the larger lactiferous ducts of the breast, as opposed to micropapillomas which affect intermediate sized ducts within the mammary parenchyma. In situ and invasive ductal carcinoma is excluded by the bland cytology of the tumor cells. The presence of desmoplasia within sclerotic papillomas creates a major pitfall for over-diagnosing breast cancer.

Multiple micropapillomas reflect proliferative breast disease, and impart an increased risk of breast cancer. This increased risk is difficult to quantify, but may approach that of conventionally defined atypical duct hyperplasia. Carcinomas arising in the setting of multiple micropapillomas tend to be of low nuclear grade.