[Diagnostic value of the BRAF variant V595E in urine samples, smears and biopsies from canine transitional cell...

Transitional cell carcinoma (TCC) is the most common malignant tumour of the canine urinary tract. Previously, the mutation of the BRAF gene V595E was identified in approximately 85 % of canine TCC cases by DNA sequencing of TCC tumour cells, both in frozen and paraffin-embedded tissue sections, as well as in urine. The objective of this study was to establish these methods in cytological smears and to investigate the prevalence of BRAF mutation V595E in canine TCC in our cohort of patients.

Biopsy samples (n = 43), urine (n = 48) and/or cytological smears (n = 31) from 66 dogs with TCC (n = 33), urinary bladder polyps (n = 7), cystitis (n = 23) or without bladder diseases (n = 3), submitted for routine diagnostics, were selected. DNA isolation from paraffin material, urine and cytological smears was performed using commercially available kits. Exon 15 was examined for the presence of the BRAF mutation c.1784T>A by Sanger sequencing.

In 39/43 paraffin-embedded biopsies and 38/48 urine samples, a sufficient amount of good quality DNA was isolated. DNA isolation and sequencing were successful in 16/18 smears with a high cell count, but not in the 10/13 smears with low cellularity. In all cases from which different sample materials were available, the results of BRAF analysis were identical in paraffin-embedded tissue, cytological smears and/or urine. In 22/31 dogs (70.9 %) with TCC, the presence of the BRAF mutation was confirmed, whereas it could not be detected in animals without pathological findings or with cystitis or with a polyp.

BRAF mutation analysis is a new and good method to be able to mostly confirm a diagnosis of TCC in uncertain cases. Non-invasive diagnostic samples, including urine and urine sediment containing sufficient numbers of relevant cells as well as cytology aspirates and formalin-fixed biopsies can be used for analysis. However, it is important to note that only a positive identification of the mutation is diagnostic. Further research is necessary to investigate prognostic and therapeutic relevance of the variant and how this genetic analysis can be used as an early detection method for TCC.