Differences of immunoreactivity for luminal and myoepithelial cell markers and oxytocin receptor in canine normal mammary ducts and ductal tumors.

Ductal tumors of canine mammary glands can be difficult to distinguish from simple tumors on routine histology. Because oxytocin receptor (OXTR) expression in myoepithelial cells has been implicated in human breast tumorigenesis, we immunohistochemically evaluated 8 ductal adenomas and 5 ductal carcinomas, including OXTR expression. Luminal cells were positive for cytokeratin 19 and pan-cytokeratin. Suprabasal myoepithelial cells were strongly positive for p63, weakly and focally positive for vimentin, and negative for smooth muscle actin and calponin, therefore indicating that p63 is the most suitable marker for these cells in ductal tumors. Unlike humans, OXTR was expressed in luminal cells of normal canine mammary ducts and in both luminal and suprabasal myoepithelial cells in ductal tumors, suggesting a role in ductal tumor development.