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 and
measurement of oestradiol hormone. The tumor was characterized by an encapsulated firm mass with a
creamy-white cut surface. Histologically, it consisted of variably-sized sinus ducts, covered by a single or
multiple 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 for
estrogen, but not for progesterone. Moreover, the high level of plasma ER concentration in contrast to the
normal PR value was consistent with immunohistochemical findings. Both results suggested that
reproductive hormones, exclusively estrogen, influenced the developmental stage of the mammary glands
and are responsible for neoplastic changes in this case. This study indicated for the first time the novel
evidence of estrogen-induced fibroadenoma in a 2-month-old lamb mammary gland tissue.