Mammary tumors are very common in female dogs and its prognosis varies significantly according to the tumor invasion degree. Myoepithelial layer destruction is considered a differential diagnosis parameter of in situ from invasive lesions in human breast cancer. Aiming to evaluate the immunohistochemical expression of p63, a protein specifically expressed by myoepithelial cells of mammary gland, and its correlation with p53 expression, 10 adenomas and 20 carcinomas with and without metastasis of canine mammary gland were studied. There was no significant difference between adenomas and carcinomas for both proteins staining, however, the percentage and continuity of staining was lower in metastatic carcinomas. There was no correlation between p53 and p63 expression, but the higher values of p53 staining were found in carcinomas, according to previous studies. Results showed that p63 is specifically expressed also in myoepithelial cells of canine mammary gland. However, in order to ensure its use as a prognostic marker in canine mammary tumors, further studies involving a higher number of samples should be conducted.
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