A 13-year-old entire male Thai Ridgeback dog presented to Prasu-Arthorn Animal Hospital, Faculty of
Veterinary Science, Mahidol University with a mass on the caudal right flank. Fine needle aspiration (FNA)
revealed round cells with intracytoplasmic granules consistent with mast cell tumour (MCT). Surgical excision
was performed. Histological grading revealed poorly-differentiated, high grade MCT with 18 mitotic figures per
10 high power-fields (HPFs) and KIT staining was consistent with KIT pattern II (focal or stippled cytoplasmic
staining); both of which are associated with poor survival. This contrasted with the better survival time
implicated by low argyrophilic nucleolar organiser region (AgNOR) and Ki-67 scores, which were all below the
cut-off values, suggesting low cellular proliferation. A chemotherapy protocol of vinblastine and prednisolone
was subsequently commenced. Distant recurrence at the neck occurred at 67 days, confirmed to be MCT by
histopathology. The dog later died, with a total survival time of 90 days from diagnosis. The actual survival time
closely aligned with the estimated survival time based on histological grading. With few multivariate survival
analyses available, this case demonstrates the use of AgNOR, Ki-67, and KIT localisation to complement
histological grading for further studies to compare different variables in a clinical setting in Thailand.
Keywords
Mast cell tumour, Grading, Ki-67, AgNOR, KIT, survival time