Canine mammary neoplasms are amongst the most common neoplastic diseases. It is assumed that reproductive hormones have an effect on tumoriogenesis, however, the precise role of the endocrine milieu and reproductive state is subject of continuing discussion. Therefore, this study investigated the association between circulating serum concentrations of estradiol-17$\beta$, progesterone and prolactin (PRL), and gene expression of estrogen receptor $\alpha$, progesterone receptor, prolactin receptor (PRLR) and growth hormone receptor, with respect to reproductive state (spayed vs. intact) and cycle stage (anestrus vs. diestrus). Furthermore, as a possible indicator of metastatic potential we evaluated the expression of E-cadherin (CDH-1), which regulates cell-cell adhesion.
The transformation from a normal to a malignant phenotype was associated with a significant loss of the gene receptor expression in the canine mammary tissue. Only PRLR in malignant tumors was significantly influenced by circulating PRL. Increased PRL levels were negatively associated with low PRLR gene expression in malignant tumors. No evidence was found for the presence of a paracrine/autocrine action of PRL in the canine mammary gland.
For CDH-1, the highest gene expression was found in benign mammary tumors in diestrous dogs compared to normal and malignant mammary tissues of anestrous and spayed dogs. Therefore it may serve as a prognostic marker.