Answer: D. Lactating Adenoma

Histology:
The core needle biopsy of the breast reveals nodular arrangement of dilated, hyperplastic terminal ducts and lobules whose cells display prominent lactational (secretory) change, characterized by vacuolated cytoplasm, occasional hobnail appearance of the cells, and punctate nucleoli. Some of the dilated lobules contain pale pink secretions.

Discussion:
The patient is a pregnant female with a new firm, mobile breast mass. The core biopsy reveals characteristic features of a lactating adenoma (also termed “nodular lactational hyperplasia”), which occur during pregnancy and the post-partum period. These lesions are typically well circumscribed and clinically resemble fibroadenomas. The appearance of the nucleoli within the nuclei can initially appear alarming, however the nucleoli are punctate, the nuclei are fairly small and uniform and the associated secretions are reassuring. The differential diagnosis of benign lactational or secretory change is hypersecretory cystic hyperplasia, which contains dilated cystic spaces, and atypical hypersecretory cystic hyperplasia, which displays cytologic atypia such as nuclear enlargement and prominent nucleoli. Focal secretory or lactational-like change can also be seen in the benign breast tissue of non-pregnant or non-lactating patients as well.

References:
1. O’Hara MF, Page DL. Adenomas of the breast and ectopic breast under lactational influences. Hum Pathol. 1985 Jul;16(7):707-12.