Effective detection of BRAFmutation in canine urothelial and prostate carcinomas using immunohistochemistry.

Abstract

Canine urothelial carcinoma (UC) and prostate carcinoma (PC) frequently exhibit the BRAFmutation, akin to the BRAFmutation common in various human cancers. Since the initial discovery of the BRAF mutation in canine cancers in 2015, PCR has been the standard method for its detection in both liquid and tissue biopsies. Considering the similarity between the canine BRAFand human BRAFmutations, we hypothesized that immunohistochemistry (IHC) using a BRAF-specific antibody could effectively identify the canine mutant BRAFprotein. We tested 122 canine UC (bladder n = 108, urethra n = 14), 21 PC, and benign tissue using IHC and performed digital droplet PCR (ddPCR) on all 122 UC and on 14 IHC positive PC cases. The results from ddPCR and IHC were concordant in 99% (135/136) of the tumours. Using IHC, BRAFwas detected in 72/122 (59%) UC and 14/21 (65%) PC. Staining of all benign bladder and prostate tissues was negative. If present, mutant BRAF staining was homogenous, with rare intratumour heterogeneity in three (4%) cases of UC. Additionally, the BRAFmutation was more prevalent in tumours with urothelial morphology, and less common in glandular PC or UC with divergent differentiation. This study establishes that BRAF-specific IHC is a reliable and accurate method for detecting the mutant BRAFprotein in canine UC and PC. Moreover, the use of IHC, especially with tissue microarrays, provides a cost-efficient test for large-scale screening of canine cancers for the presence of BRAF mutations. This advancement paves the way for further research to define the prognostic and predictive role of this tumour marker in dogs and use IHC to stratify dogs for the treatment with BRAF inhibitors.