Mast cell tumors (MCTs) are the second most common skin tumor in cats, comprising up to 21% of all skin tumors in cats. The etiology of MCTs is unknown though some prior studies cite a possible genetic predisposition in Siamese cats.
There is currently no histological grading system for MCTs in cats, unlike in dogs, therefore a more accurate prognosis for disease outcome is difficult to determine. The tumors are classified as one of three histological types: well-differentiated mastocytic, pleomorphic mastocytic, and atypical (previously referred to as histiocytic). The majority of feline cutaneous MCTs arise as a single, well-differentiated, and benign mass often cured by complete surgical excision. A small yet significant portion of these tumors are more aggressive and can recur and/or metastasize to local lymph nodes or other distant sites within months of excision. The investigators in this study aimed to use a large number of histological samples of cutaneous MCTs to examine signalment and anatomical location of the tumors, in an attempt identify potential indicators of the course and outcome of the disease.
The numbers of cutaneous MCTs submitted were from 287 cats with 308 tumors. Eighty-six tumors from 69 cats - with a known outcome - were then evaluated by follow up. The anatomic locations were categorized as one of the following: head (including the ear), neck and trunk, or extremities (including limbs, paw, and tail). The locations were then subcategorized as head, ear, neck, trunk, limbs, paw or tail. The results of the study in regards to anatomical location of lesions showed the head, including the ear, was the most common site over all (38.1%), followed by the neck and trunk (33.3%). The extremities (limbs, paws and tail) accounted for the remaining number (28.5%). Of the 11 Siamese cats (other breeds considered at increased risk are Burmese, Russian Blue and Ragdoll cats) in the study population, the head was the overwhelming primary location of MCTs. In cats seven years of age or less, MCTs were more likely to be found on the head; with older cats 8 years of age or older were more likely to have lesions arise on the trunk.
On histological evaluation, fifty-seven (66.3%) of MCTs were classified as well-differentiated mastocytic type. A novel subcategory (five cats, 5.8%) of the well-differentiated MCT type was noted with prominent multinucleated cells. These cells were larger and most often present in the periphery of the mass and contained more than two nuclei per cell. Seventeen (19.8%) of MCTs were classified as pleomorphic mastocytic followed by seven (8.1%) classified as the atypical type. Multiple cutaneous MCTs (either arising simultaneously, sequentially or a mix of both) occurred in 10 cats.
Some of the key findings from the study:
