Coincidence of v-raf murine sarcoma viral oncogene homolog B mutation (V595E) with phosphorylated v-raf murine sarcoma viral oncogene homolog B in urothelial carcinoma in dogs.

Expression of phosphorylated v-raf murine sarcoma viral oncogene homolog B (pBRAF) and phosphorylated extracellular signal-regulated kinase1/2 (pERK1/2) were investigated in urothelial carcinoma (UC) in dogs with or without the BRAF gene mutation (V595E). Among the 10 cases of UC with V595E (-), cytoplasmic immunoreactivity against pBRAF of neoplastic cells was reported in 8, with 7 displaying moderate reactivity and 1 displaying intense reactivity. Nuclear immunoreactivity against pBRAF was detected in 5 cases; however, these reactivities were non-specific, due to pBRAF being limited in the cytoplasm. In addition, positive cytoplasmic immunoreactivity against pERK1/2 of neoplastic cells was detected in 7 cases and nuclear immunoreactivity against ERK1/2 was detected in 6 cases. Among the 13 cases of UC with V595E (+), cytoplasmic immunoreactivity against pBRAF of neoplastic cells was detected in all 13 cases and nuclear immunoreactivity against pBRAF was detected in 10 cases; however, the nuclear immunoreactivity was non-specific. Cytoplasmic immunoreactivity against pERK1/2 of neoplastic cells was detected in all 13 cases and nuclear immunoreactivity against pERK1/2 was also detected in all cases. As nuclear pERK1/2 indicates a progressive signaling process in the mitogen-activated protein kinase pathway, V595E (+) UC might be in its growing stage. Probable phosphorylated sites of pBRAF at Thr598/Ser601, detected in this study, are major and essential sites of the upstream rat sarcoma viral oncogene homolog (RAS) signaling pathway. In human cancers, the BRAF mutation never coincides with oncogenic RAS. To our knowledge, this is the first report on the simultaneous occurrence of the BRAF mutation (V595E) and pBRAF expression (at Thr598/Ser601) in dogs with UC with V595E (+).