Mesenchymal tumors consist of individualized generally spindle shaped cells with indistinct cytoplasmic borders that “fade” into the background. In this aspirate of a skin mass in a cat, some of the tumor cells are distinctly spindled but others are more round. Interspersed macrophages (arrow) also complicate the cytologic picture. Note the large nucleus and two indistinct nucleoli that are of variable size in the spindled cell in the middle, both of which are features of malignancy. This was a good example of a vaccine-induced sarcoma (Wright’s stain, 100x objective).
