Clinical Outcome and Histopathologic Assessment of Canine Perivulvar Mast Cell Tumours

Anatomic location is a known prognostic factor for canine mast cell tumours (MCTs). Previous publications have reported conflicting results about the clinical significance of MCT location in the inguinal and perineal regions and male genitalia. Hence, the goal of this study is to evaluate the grade, breed distribution and clinical outcome of canine perivulvar MCT. Surgical biopsy reports and associated medical records submitted between 2013 and 2024 to Michigan State University Veterinary Diagnostic Laboratory were retrospectively evaluated. Information regarding age, reproductive status, breed, tumour location, microscopic description, histopathologic grade, and survival was collected. Kaplan-Meier analysis was used to estimate median survival time (MST) with dogs lost to follow-up (LTF) or alive censored from analysis. Biopsy reports from 64 dogs with 68 perivulvar MCT were evaluated. The most common phylogenetic classification was Mastiff-Terrier (47%). The majority (97%) of evaluated MCT were cutaneous, with 85% categorised as Kiupel low grade, while the remaining 15% were high grade. Three of 19 tumours (16%) that had c-KIT PCR performed had mutations in either Exon 8 or Exon 11. KIT expression pattern was classified as Pattern 2 or 3 in 71% of evaluated tumours. Median Ki-67 proliferation index and Ki-67 × AgNOR scores were 7 and 13, respectively. MST for the entire population was 868 days. Dogs LTF had a median follow-up time of 442 days. Dogs with perivulvar MCT may achieve prolonged survival time with surgical excision, and prospective studies are warranted to determine the effect of adjuvant therapy on outcome.