BRAF V600E mutations in right-side colon cancer: Heterogeneity detected by liquid biopsy.

INTRODUCTION: The prognosis for metastatic colorectal cancer patients (mCRC) with the BRAFV600E mutation is poor. BRAFV600E mutation frequency is reportedly low among Asians; however, the frequency of the BRAFV600E mutation in right-side colon cancer may not be low, even among Asians. In addition, spatial heterogeneity of BRAFV600E mutations also exists, as for RAS mutations. In this prospective observational study, we evaluated BRAFV600E mutations in cancer tissue and plasma of Japanese right-side colon cancer patients. METHOD: 215 patients with right-side colon cancer were included. BRAFV600E mutations of cancer tissue and plasma were detected using droplet digital PCR. Blood plasma of patients with BRAFV600E mutations in cancer tissue or plasma was drawn at intervals throughout chemotherapy, and BRAFV600E mutations were evaluated. RESULTS: BRAFV600E mutations were detected in tissue samples from 35 of 215 patients (16.3%, cecum; 22.4%, ascending colon; 17.8%, and transverse colon; 9.0%). BRAFV600E mutations were detected in plasma of 10 of 215 (4.7%) patients. Eight of the ten patients had BRAFV600E mutations in their primary tumours, but two (both were Stage IV) patients did not. Sensitivity of liquid biopsy to detect BRAFV600E mutations was 10.3% (3/29) in Stage I-III patients and 83.3% (5/6) in Stage IV patients. CONCLUSION: BRAFV600E mutations are observed in right-side colon cancer at high frequency, especially in the cecum. BRAFV600E mutations can be detected in plasma and the detection rate is high in patients with advanced cancer. Spatial heterogeneity was observed using liquid biopsy.