Based on a recent cytology grading system proposed by Camus and colleagues, canine cutaneous mast cell tumours can be graded cytologically and being classified as low or high grade, based on the presence / absence of specific morphological features. The algorithm below taken from the original publication shows the criteria used for grading purposes.
Cutaneous mass, Dog, High grade mast cell tumour, Wright Giemsa, 50x
The cytologic algorithm that most closely correlated with histologic grade classified a MCT as high grade if it is (1) poorly granular or (2) has at least 2 of the following 4 features: presence of any mitotic figures, anisokaryosis, binucleation or multinucleation, or nuclear pleomorphism. This system showed a good correlation with clinical behaviour and cytologic high grade tumours were associated with significantly decreased probability of survival. However, both false positive and false negative results occurred, suggesting histopathology grading is still recommended after surgical removal of the mass. Histopathology will also provide important further information, such as surgical margins. In selected cases, from the histology sections it is also possible evaluating proliferative markers (e.g. Ki67) which can provide additional prognostic information.