EPOR and breast cancer: It has been shown an increase in the number and distribution of Epor and Tryptase-positive MCs in the peritumoral stroma both in the normal/hyperplastic and neoplastic canine mammary glands tumors [19] and that tryptase positive MCs in canine mammary tumors are directly involved in the activation of metalloproteases, thus promoting the degradation of the extracellular matrix as well as the proliferation of vascular endothelial cells and cell differentiation [20].