Immunohistochemical markers allow the determination of the presence of hormone receptors (estrogen receptor, progesterone receptor), the cell proliferation rate (Ki-67), angiogenesis (VEGF, CD31, CD34), and pro-angiogenic determinants such as the COX-2 enzyme, as well as the evaluation of markers indicative of tumor aggressiveness, such as the expression of receptors for epidermal growth factors (EGFR and HER-2) and transcriptional markers of proliferation and epithelial–mesenchymal transition (c-Kit, cadherins, CD44, ZEB1 and 2, TWIST) in female dogs [89]. This evidence concerns the gene MKI67 and neoplasm.