Young Cat with Large Mammary Glands...What is it Called?

Feline mammary fibroepithelial hyperplasia.

In this condition, young estrous-cycling or pregnant cats (or any cat exposed to progesterone) develop rapid enlargement of the mammary glands. This can look WILD where the cat all of a sudden has huge, sometimes even ulcerated mammary glands.

Cytologically, there is a combination of benign/hyperplastic epithelial cells and mesenchymal cells, like we see in this photo. Neat huh?!