Detection of Colorectal Cancer and Advanced Adenoma by Liquid Biopsy (Decalib Study): The ddPCR Challenge

Abstract

Background: In most countries, participation in colorectal cancer (CRC) screening programs with the immunological fecal occult blood test (iFOBT) is low. Mutations of RAS and BRAF occur early in colorectal carcinogenesis and "liquid biopsy" allows detection of mutated circulating tumor DNA (ctDNA). This prospective study aims to evaluate the performance of RAS and BRAF-mutated ctDNA in detecting CRC and advanced adenomas (AA).

Methods: One hundred and thirty patients who underwent colonoscopy for suspicion of colorectal lesion were included and divided into four groups: 20 CRC, 39 AA, 31 non-advanced adenoma and/or hyperplastic polyp(s) (NAA) and 40 with no lesion. Mutated ctDNA was analyzed by droplet digital PCR.

Results: ctDNA was detected in 45.0% of CRC, in 2.6% of AA and none of the NAA and "no-lesion" groups. All patients with stage II to IV mutated CRC had detectable ctDNA (n = 8/8). Among the mutated AA, only one patient had detectable ctDNA (4.3%), maybe due to limited technical sensitivity or to a low rate of ctDNA or even the absence ctDNA in plasma. Specificity and sensitivity of KRAS- and BRAF-mutated ctDNA for the detection of all CRC and AA were 100% and 16.9%, respectively.

Conclusions: ctDNA had high sensitivity in detection of advanced mutated CRC but was unable to sensitively detect AA. ctDNA analysis was easy to perform and readily accepted by the population but requires combination with other circulating biomarkers before replacing iFOBT.

Keywords: circulating tumor DNA; colorectal cancer; droplet digital PCR; fecal occult blood test; liquid biopsy.

Figure 1

Flowchart. CRC group: colorectal cancer, AA group: patients with at least one advanced adenoma, NAA group: patients with non-advanced adenoma(s) and/or hyperplastic polyp(s), no-lesion group: patients with no colorectal lesion, cfDNA: circulating free DNA, AA: advanced adenoma, NAA: non-advanced adenoma, HP: hyperplastic polyps.

Figure 2

Box plots for the distribution of circulating free DNA concentrations in each group by QuantiFluor^®. Each box indicates the 25th and 75th percentiles. The horizontal line inside the box indicates the median and the whiskers the extreme measured values. The Mann–Whitney test was performed for determination of statistical significance. * p < 0.05; ** p < 0.01. Normal: no lesion group; NAA: non-advanced adenoma group; AA: advanced adenoma group; CRC: colorectal cancer group.