Mast cell tumor (MCT) is the most common malignant cutaneous neoplasm in dogs. Even with several prognostic markers being studied, in attempt to previse the biological behavior of these tumors, the histological grading is still commonly used to predict behavior, however, it is not significant to predict intermediately differentiated MCT behavior. Different prognostic and cell proliferation markers are being tested with promising results however, the majority of then requires specific staining and immunohistochemical techniques that even nowadays are expensive and not suitable for all veterinarians. Mitotic index is an indirect measure of cell proliferation and it can be established in a common histological microscope slide, and studies indicate it as an important prognostic marker for MCT in dogs. Given the recent publication of the novel two-tier histologic grading system, this study objective to evaluate the prognostic value of the different grading systems associating with survival and compare it with the mitotic index. Even though both grading systems associate with survival in the univariable analyses (P<.001), at the multivariable analyses neither was associated with survival (P>0,05), and the mitotic index was the most significant prognostic factor for survival, regardless of the cut-off point used (P<0,05), especially when Patnaik grade 2 tumors with unpredictable biological behavior were analyzed. The mitotic index was also significantly associated with both local and distant reccurence and paraneoplastic syndrome. In this study, mitotic index was the most significant prognostic factor, in the absence of specific staining and advanced immunohistochemical techniques, and its use is indicated in association with both histological grading system, aiming to add higher prognostic value possible.
Cutaneous mast cell tumor; prognostic markers; mitotic index; dogs
