[The ultrastructure of mixed mammary gland tumors in bitches. IV. The incidence of myoepithelial cells in formation of spindle cells (author's transl)].

Spindle cells of myomatous formations of 19 canine mixed mammary tumors were studied by light and electron microscopy. The EM findings indicate that the spindle-shaped tumor cells are mostly of myoepithelial origin. However there were also formations of spindle cells which consisted of fibroblasts or fibrocytes. By light microscopy they are not always clearly distinguishable.