BRAF V600E-specific immunohistochemistry reveals low mutation rates in biliary tract cancer and restriction to intrahepatic cholangiocarcinoma

Abstract

BRAF mutations have emerged as an important predictive biomarker for metastasized melanoma. Other types of cancer may also benefit from BRAF mutation-targeted therapies. In biliary tract cancer, reported BRAF mutation rates are highly controversial, ranging from 0 to 33% in adenocarcinoma of the gallbladder and 0 to 22% in cholangiocarcinoma. We here analyzed tissue microarrays of a large cohort of biliary tract cancer (n ¼ 377) including 159 intrahepatic cholangiocarcinomas, 149 extrahepatic cholangiocarcinomas, and 69 adenocarcinomas of the gallbladder for BRAF V600E mutation using a highly sensitive immunohistochemical screening approach implementing the BRAF V600E protein-specific antibody VE1. All VE1-positive cases as well as 42 VE1-negative cases were additionally analyzed by Sanger sequencing. In total, only 5 VE1-positive cases were detected (5/377; 1%). BRAF V600E mutation was confirmed by direct sequencing in all cases. All 5 mutated cases were intrahepatic cholangiocarcinomas (5/159; 3%). None of the extrahepatic cholangiocarcinomas and adenocarcinomas of the gallbladder were VE1 positive. Apart from the subtype restriction of BRAF V600E mutation to intrahepatic cholangiocarcinoma and a female predominance (4 female, 1 male), no significant correlation with clinicopathological data and patient outcome was detected. In conclusion, we demonstrate that BRAF V600E mutation is a rare event in biliary tract cancer, accounting for only 1% of all subtypes, and is restricted to intrahepatic cholangiocarcinoma. In addition, we demonstrate that VE1 immunohistochemistry is a feasible approach to routinely screen for BRAF V600E mutation in biliary tract cancer patients, thereby facilitating the detection of rare patients who may benefit from BRAF mutation-targeted therapies.

Impressive response to dual BRAF and MEK inhibition in patients with BRAF mutant intrahepatic cholangiocarcinoma—2 case reports and a brief review

“…The frequency of BRAF mutations in ICC have ranged between 1% to 22% among various cases series or population studies. The frequency appears to be underestimated when assessed by immunohistochemistry studies in comparison to PCR (6,7). In addition, the variations in the reported frequency may be related to differences in PCR techniques and Next Generation Sequencing (NGS) as well as distinct differences in the study populations.…”

Cholangiocarcinoma — evolving concepts and therapeutic strategies

“…Neither of these studies involved patient selection based on KRAS mutation status. BRAF mutations can also occur in cholangiocarcinoma (predominantly in iCCAs), albeit at a low frequency (3–5%) 102,113,116 . In eight patients with BRAF V600-mutated cholangiocarcinoma, treatment with the oral BRAF inhibitor vemurafenib led to a partial response in one patient 117 .…”

Clinical and biological significance of precursor lesions of intrahepatic cholangiocarcinoma

“…Interestingly, both wild-type BRAF and BRAF V600E lesions coexisted in patients with multiple BDAs. Identification of oncogenic mutations in BDA supports a benign neoplasm rather than reactive process and suggests that BDA may be an early lesion in the pathogenesis of ICC, which has been shown to harbor BRAF V600E mutations [54,55] . Furthermore, the finding of coexistence of benign lesions, dysplastic lesions and carcinoma (authors' unpublished data) and progression of BDA to ICC [9] strongly suggests an adenoma-dysplasia-carcinoma pathway, as seen in colorectal carcinogenesis.…”