Endometrial stromal sarcoma with smooth muscle and glandular differentiation of the feline uterus

The intra-abdominal tumor developing in the uterus and lung of a domestic Shorthair cat was examined histopathologically and immunohistochemically. The tumor showed a proliferation of both endometrial stromal and smooth muscle cells accompanied by prominent vasculature. There were well-differentiated endometrial glands, and tubuli made up a monolayer of eosinophilic cuboidal epithelium. Immunohistochemically, the spindle-shaped cells and half of the stromal-like cells reacted to caldesmon and desmin antibodies. The neoplastic epithelium expressed AE1/AE3 cytokeratin. Feline endometrial stromal tumor has, to the best of our knowledge, not been reported previously and has smooth muscle and glandular components that are a unique variant to the human counterpart.