Immunohistochemical determination of estrogen receptor-α in vaginal and tumor tissues of healthy and TVT-affected bitches and their relation to serum concentrations of estradiol-17β and progesterone

One of the most frequent canine neoplasms is the transmissible venereal tumor (TVT), which affects the male and the female genital tract. The objective of this study was to determine (immunohistochemically) estrogen receptor (ER-α) expression in vaginal tissue of healthy bitches and in the vaginal and neoplastic tissues of TVT-affected bitches. Fifty-eight bitches were divided into two groups: tumor group (TVT) and control group (healthy). Canine estrous cycle stages were determined by means of exfoliative vaginal cytology, hormone assays, and macroscopic appearance of ovaries. Samples from vaginal and neoplastic tissues were obtained under general anesthesia, fixed in 10% buffered formaldehyde, embedded in paraffin, and sectioned. Anestrus, proestrus and estrus control females had higher ER-α expression than diestrus bitches. Within the tumor group, diestrus bitches had significantly higher ER-α expression. Although some samples had expression in the endothelium of blood vessels, no ER-α expression was observed in neoplastic tissues. In conclusion, vaginal tissue of tumor and control bitches, under different distinct steroid influences, had different ER-α expression, whereas ER-α expression was not present in neoplastic tissues.