Cancer-associated fecal microbial markers in colorectal cancer detection

Abstract

Colorectal cancer (CRC) is the second most common cause of cancer death in the western world. An effective screening program leading to early detection of disease would severely reduce the mortality of CRC. Alterations in the gut microbiota have been linked to CRC, but the potential of microbial markers for use in CRC screening has been largely unstudied. We used a nested case-control study of 238 study subjects to explore the use of microbial markers for clbA+ bacteria harboring the pks pathogenicity island, afa-C+ diffusely adherent Escherichia coli harboring the afa-1 operon, and Fusobacterium nucleatum in stool as potential screening markers for CRC. We found that individual markers for clbA+ bacteria and F. nucleatum were more abundant in stool of patients with CRC, and could predict cancer with a relatively high specificity (81.5% and 76.9%, respectively) and with a sensitivity of 56.4% and 69.2%, respectively. In a combined test of clbA+ bacteria and F. nucleatum, CRC was detected with a specificity of 63.1% and a sensitivity of 84.6%. Our findings support a potential value of microbial factors in stool as putative noninvasive biomarkers for CRC detection. We propose that microbial markers may represent an important future screening strategy for CRC, selecting patients with a "high-risk" microbial pattern to other further diagnostic procedures such as colonoscopy.

Keywords: F. nucleatum; clbA; colorectal cancer; gut microbiota; screening; stool.

Figure 1

Flow chart describing the FECSU cohort and the selection of study subjects.

Figure 2

Bacteria carrying clbA are abundant in stool of CRC patients. Differences in absolute number (n) and percentage (%) of (a) clbA‐ and (b) afaC‐positive stool samples between controls, and patients diagnosed with dysplasia or cancer are illustrated.

Figure 3

Increased levels of F. nucleatum are detected in stool of CRC patients. (a) A Beeswarm Boxplot is used to illustrate the relative levels of F. nucleatum in stool of control patients, and patients diagnosed with dysplasia or cancer. Horisontal lines indicate median (in bold) and quartiles. (b) An ROC curve displaying the specificity and the sensitivity for the F. nucleatum assay. The ROC curve was calculated using the variable for F. nucleatum and cancer/no cancer. The level of F. nucleatum in each sample is given as a relative quantification with the total microbial 16S rRNA gene DNA in each sample as reference 2^{∧ (−ΔCq)}, ΔCq = Cq^{F. nucleatum} − Cq16^{S rRNA gene}).