Answer: Fibroadenoma with sclerosing adenosis and ductal carcinoma in situ

Histology: The underlying lesion is a fibroadenoma having myxoid stroma, in which there are central glands with an intracanalicular, indented pattern surrounded by clusters of tubules in a lobular distribution. In much of the lesion, the tubules are distorted, in that they are centrally sclerotic and open up at the periphery, which is typical of superimposed sclerosing adenosis in a fibroadenoma. However, in one area of the lesion there is a monotonous cribriform proliferation of luminal cells. These cells expand the otherwise compressed tubules of the superimposed sclerosing adenosis. These uniform hyperchromatic cells form cribriform spaces which extent over an area of greater than 3mm, and that’s diagnostic of ductal carcinoma in situ, low grade, involving a complex fibroadenoma.

Discussion: Usual ductal hyperplasia would feature more polymorphous epithelium, which typically has hypochromatic nuclei and forms irregular slit like spaces. Simple fibroadenomas or fibroadenomas with sclerosing adenosis lack the uniform cribriform epithelial proliferation seen in the current case.