Pathological features of fibrous proliferative lesions of the vagina in dogs.

The clinical, histological, and immunohistochemical features of 26 fibrous proliferative lesions in the vagina of 14 female dogs (13 intact and 2 neutered) were examined. These lesions presented as nodular or pedunculated masses. Histopathological examination revealed that all lesions consisted of spindle- and stellate-shaped cells with mild atypia, collagenous stroma, and blood vessels. Mitotic figures were rare. The number of blood vessels was significantly greater in pedunculated masses than in nodular masses. Immunohistochemically, spindle- and stellate-shaped cells were positive for progesterone receptor in all 26 lesions, estrogen receptor in 5 of 26 lesions, desmin in 20 of 26 lesions, and α-smooth muscle actin (αSMA) in 8 of 26 lesions. Lesions in neutered dogs exhibited lower progesterone receptor expression and higher estrogen receptor expression than those in intact females. No significant differences in desmin or αSMA expression were observed between the two groups. These findings suggest that the fibrous proliferative lesions in the canine vagina described in this study may represent progesterone-associated benign proliferative changes composed of myofibroblasts.