Ki67 index in canine dermal mast cell tumours: do we only identify proliferating mast cells?

Abstract

Biopsies from 92 dogs with TCC were routinely processed for histopathology and graded into low grade or high grade, according to Meuten & Meuten (2017). DNAisolation from paraffin embedded material was performed with the use of commercially available sets. Exon 15 was examined for the presence of the BRAF variant c.1784T > A by TaqMan ® SNP Assay. RESULTS 64/92 TCCs were classified as high grade and 28/92 as low grade. BRAF mutation was found in 33/64 (51.5%) of the high grade and in 12/28 (42.8%) of low grade TCCs. STATEMENT (CONCLUSIONS) BRAF variant analysis is a new, highly specific diagnostic test for TCC. However, it is important to note that only identification of the mutation is diagnostic. It must be taken into consideration that histologically low grade TCCs showed the mutation in only about 40% of the cases. Further studies of clinical outcome are ongoing to evaluate the prognostic relevance of this finding. Additional factors, such as breed and anatomical site of the neoplasm may also influence the prevalence of BRAF mutation.