Use of p63, a myoepithelial cell marker, in determining the invasiveness of spontaneous mammary neoplasia in a rhesus macaque (Macaca mulatta).

Here we describe a case of mammary gland ductal carcinoma in an aged rhesus macaque. Tumors were diagnosed based on routine hematoxylin and eosin staining. Invasiveness was further characterized by p63 immunohistochemistry. p63 is a p53 homolog that strongly and specifically stains nuclei of myoepithelial cells in human and canine mammary tissue. Because p63 has an affinity for the nucleus of myoepithelial cells, it is readily visible. Staining of mammary tissue from the monkey for p63 revealed that multiple foci of neoplastic cells had breached the myoepithelial cell layer surrounding ducts, suggesting the potential for local invasion of the tumor. Regional metastasis was confirmed at necropsy. To our knowledge, this is the first documented use of p63 for effectively determining the invasive nature of a mammary tumor in a nonhuman primate and the first use of p63 as an effective means of staining myoepithelial cells in a mammary ductal carcinoma in a nonhuman primate. Because nonhuman primates are important animal models for human diseases, including neoplasia, this method may prove useful for both diagnostic and research purposes.