Canine mammary ductal tumors show distinct OXTR expression patterns, with p63 as a superior myoepithelial marker.

Distinguishing ductal tumors from simple tumors in canine mammary glands using routine histology remains a diagnostic challenge. In human breast tumorigenesis, oxytocin receptor (OXTR) expression in myoepithelial cells has been implicated, suggesting a potential role in tumor development. However, the specific expression patterns of myoepithelial cell markers and OXTR in canine mammary ductal tumors, and how they compare to human pathology, are not well-defined, hindering accurate diagnosis and understanding of disease progression.

Researchers immunohistochemically analyzed 8 ductal adenomas and 5 ductal carcinomas from canine mammary glands. They evaluated the expression of several luminal cell markers (cytokeratin 19, pan-cytokeratin) and myoepithelial cell markers (p63, vimentin, smooth muscle actin, calponin), in addition to OXTR expression. This approach aimed to identify reliable diagnostic markers and characterize the OXTR profile in canine ductal tumors compared to normal mammary ducts.

Luminal cells consistently showed positivity for cytokeratin 19 and pan-cytokeratin. Suprabasal myoepithelial cells were strongly positive for p63, while showing only weak and focal positivity for vimentin. They were notably negative for smooth muscle actin and calponin, indicating p63 as the most suitable marker for these cells in canine ductal tumors. A key finding regarding OXTR expression revealed a significant species difference: > Unlike humans, OXTR was expressed in luminal cells of normal canine mammary ducts and, importantly, in both luminal and suprabasal myoepithelial cells within canine ductal tumors. This suggests a distinct role for OXTR in canine ductal tumor development.