Extended RAS and BRAF mutation analysis of circulating tumor DNA in patients with biliary tract cancer

Background

Clinical trials have failed to show benefit from adding anti-EGFR antibodies to chemotherapy in the systemic treatment of biliary tract cancer with respect to progression free and overall survival, but a trend towards higher response rate. In colorectal cancer, effect of anti-EGFR therapy is restricted to patients with RAS and BRAF wild-type tumors. Mutation analysis of circulating DNA may be a clinically applicable method for serial analyses. The purpose of this early cancer biomarker study was to evaluate the feasibility of extended RAS and BRAF mutation analysis of cell free DNA in blood derived from patients with metastatic biliary tract cancer.

Methods

Patients with KRAS exon 2 codons 12/13 wild type metastatic biliary tract cancer and available blood samples were included. DNA was isolated from 4 ml plasma, pre-amplified and analyzed using Droplet Digital PCR. Adequate positive and negative controls were included. The extended RAS and BRAF analysis covered a total of 27 mutations in KRAS exons 3/4, NRAS exon 2/3 and BRAF V600E.

Results

A total of 52 patients were included. In 12 patients (23.1%), a mutation was found; BRAF n = 4, KRAS n = 4 and NRAS n = 4. Except for one patient with a NRAS mutation in plasma and wild-type in tumor, tumor biopsies harbored an identical mutation.

Conclusions

Extended RAS and BRAF mutation analysis in cell free DNA from blood derived from patients with metastatic biliary tract cancer was feasible. The fraction of mutations was 23.1% and equally distributed in KRAS, NRAS and BRAF. The high frequency of mutations beyond KRAS exon 2 may explain the lacking effect of EGFR inhibition in previous studies and justify extended mutation analysis.

Clinical trial identification

NA

Legal entity responsible for the study

Lars Henrik Jensen

Funding

Lillebaelt Hospital

Disclosure

All authors have declared no conflicts of interest.