Carcinoembryonic antigen (CEA) is a useful biomarker for colorectal cancer patients undergoing curative surgery or chemotherapy. However, ∼30% of metastatic colorectal cancer patients are CEA-negative. The use of more sensitive biomarkers might improve patient outcomes, but no candidates are currently available. Recently, circulating cell-free DNA (ccfDNA) was detected in the peripheral blood of cancer patients, and was used to detect KRAS mutations. Here, we evaluated mutant KRAS detection in ccfDNA as a means of monitoring disease progress.
We enrolled 45 colorectal cancer patients (15 with KRAS mutant and 30 with KRAS wild-type primary tumours) with distant metastases. ccfDNA was purified from 1 mL plasma using the QIAamp Circulating Nucleic Acid Kit. We detected nine KRAS mutations (G12A, G12R, G12D, G12C, G12S, G12V, G13D, Q61H, and Q61R) using digital PCR. We evaluated ccfDNA KRAS mutations every 2 months during chemotherapy or after curative surgery. The study protocol was approved by the Ethics Review Committee of our institution. Written informed consent was obtained from each patient.
KRAS mutations in ccfDNA were detected in 87% (13/15) of patients with KRAS mutation in their primary tumour, but in only 10% (3/30) of patients without KRAS mutations. We administered chemotherapy to 16 patients with KRAS wild-type primary tumours, and nine patients whose primary tumours were KRAS mutant-type. One KRAS mutant patient underwent resection of the metastatic liver tumour after chemotherapy. We detected tumour recurrence or an increase in tumour size in two primary KRAS mutant patients and two primary KRAS wild-type patients. The two primary KRAS mutant patients showed increased copy numbers of mutated KRAS in their ccfDNA. Surprisingly, we detected KRAS mutations in ccfDNA of the two KRAS wild-type patients.
The detection of KRAS mutations in ccfDNA is non-invasive and repeatable. It appears to be useful for patients with KRAS-mutated tumours as well as those with KRAS wild-type tumours, and has the potential to be a biomarker for disease progression.
Clinical trial identification
All authors have declared no conflicts of interest.