Estrogen-induced mammary fibroadenoma in a lamb: hormonal and immunohistochemical aspects

A fibroadenoma was diagnosed in the mammary gland of a lamb by immunohistochemical method andmeasurement of oestradiol hormone. The tumor was characterized by an encapsulated firm mass with acreamy-white cut surface. Histologically, it consisted of variably-sized sinus ducts, covered by a single ormultiple layers of proliferated epithelial cells, and embedded in a loose connective tissue. Immunohistochemical results revealed that more than half of the epithelial tumor cells were labelled only forestrogen, but not for progesterone. Moreover, the high level of plasma ER concentration in contrast to thenormal PR value was consistent with immunohistochemical findings. Both results suggested thatreproductive hormones, exclusively estrogen, influenced the developmental stage of the mammary glandsand are responsible for neoplastic changes in this case. This study indicated for the first time the novelevidence of estrogen-induced fibroadenoma in a 2-month-old lamb mammary gland tissue.