Immunoexpression of Steroid Hormone Receptors and Proliferation Markers in Uterine Leiomyoma and Normal Myometrial Tissues from the Miniature Pig, Sus scrofa

Uterine leiomyomas in miniature pet pigs occur similarly to those in women with regard to frequency, age, parity, and cycling. Clinical signs, gross, and histologic features of the porcine tumors closely resemble uterine leiomyomas (fibroids) in women. Although fibroids are hormonally responsive in women, the roles of estrogen and progesterone have not been fully elucidated. In this study, immunohistochemistry was used to assess the expression of the steroid hormone receptors, estrogen receptor alpha (ER-), estrogen receptor beta (ER-) and progesterone receptor (PR), and cell proliferation markers, proliferating cell nuclear antigen (PCNA) and Ki-67 in tumor and matched myometrial tissues sampled from miniature pigs. A quickscore method was used to determine receptor expression and labeling indices were calculated for the markers. ER-/ and PR were localized to the nuclei of smooth muscle cells in both tissues. PR expression was intense and diffuse throughout all tissues, with correlation between tumors and matched myometria. Conversely, ER- expression was variable between the myometrial and tumor tissues, as well as between animals. ER- expression was low. PCNA and Ki-67 were localized to the nucleus and expression varied among tumors; however, normal tissues were overall negative. These findings support further investigation into the use of the miniature pig as a model of fibroids in women.