Canine mast cell tumors: utility of stereologic tools in cytology.

Quantitative morphologic parameters assessed in cytologic samples of canine cutaneous mast cell tumors (ccMCTs) may assist with surgical planning and prognostication. Robust cutoffs can be defined, with high reproducibility, for parameters such as the nuclear area (NA). The NA may be determined by morphometry (image analysis, NAI) or by stereology, such as the 2D-nucleator method (NAN); stereologic techniques have not been applied to cytologic specimens of ccMCT, to our knowledge. We retrospectively selected routine cytology smears from 51 ccMCT cases and screened them to determine the percentage of neoplastic mast cells with indistinct nuclear borders; this was repeated after the slides were restained with H&E. The NAI and the NAN were estimated in 100 mast cells per animal in H&E-stained slides. All nuclei were visible in H&E smears, and unbiased quantification was feasible. The NAN was similar to NAI, but less time-consuming. Both the NAN and NAI determined by cytology differed in histologic low- and high-grade ccMCTs, and in histologic grade I plus II versus grade III ccMCTs. Stereologic parameters such as the NAN could be considered as complementary techniques for the cytologic evaluation of ccMCTs.