Progesterone receptor expression and proliferative activity in relation to histological architecture of feline mammary fibroadenomatous change

The aim of the study was to determine the relationship between histological architecture and progesterone receptor expression as well as proliferative activity in feline mammary fibroadenomatous change (FMFAC) in female cats. The investigations were performed on 16 surgically removed FMFAC diagnosed based on their gross and microscopic appearance. The lesions were divided into 2 groups based on the number of epithelium layers: lesions with two or less ductal epithelium layers formed group A and lesions with more than two layers of epithelial cells were assigned to group B. Moreover, in each group the lesions were classified according to the cellularity of stroma into three subgroups (with poor, moderate and abundant cellularity). Immunohistochemical examinations were carried out to detect an expression of progesterone receptors (PRs) and a proliferative activity (based on Ki-67 antigen expression). The PR expression and Ki-67 antigen expression were significantly higher in epithelial cells than in stromal cells; however, the differences in above mentioned markers in ductal epithelium and stromal cells between studied groups were not significant. The results of this study indicate that there is no relationship between histological appearance, PR expression and proliferative activity in FMFAC. Moreover, a high percentage of PR-expressing cells in duct epithelium may explain the regression of enlarged mammary gland after administration of progesterone receptor blockers.