Fig. 4: Colibactin mutagenesis as an early event in MSS colorectal cancer evolution.

a, Fold change of the relative contribution per sample of each signature between early clonal and late clonal SBSs (left) and IDs (right). SBS signatures that contribute early and late clonal SBSs in fewer than 50 samples were excluded from the analysis. Similarly, ID signatures that contribute early and late clonal IDs in fewer than 20 samples were also excluded. Signatures were sorted by median fold change. b, Lack of concordance between colibactin exposure status determined by the presence of colibactin-induced signatures SBS88 or ID18, and the microbiome pks status. Statistical significance was evaluated using a multivariable Firth’s bias-reduced logistic regression model (due to quasi-complete separation) adjusted by age of diagnosis, sex, country, tumour subsite and tumour purity. c,d, Distribution of age of onset (c) and cases across age groups (d) based on the detection of colibactin-positive samples using genomic and microbiome status. The genomic status is defined by the presence of SBS88 or ID18; the microbiome status (pks) is determined by coverage of at least half of the pks island, and suggests ongoing or active pks⁺ bacterial infection (genomic⁻ pks⁻ n = 549, genomic⁻ pks⁺ n = 82, genomic⁺ pks⁻ n = 148, genomic⁺ pks⁺ n = 21). Statistical significance was evaluated using a multivariable linear regression model adjusted by sex, country, tumour subsite and tumour purity. In box plots, the horizontal line indicates the median, the upper and lower ends of the box indicate the 25th and 75th percentiles. Whiskers show 1.5 × the interquartile range, and values outside the whiskers are shown as individual data points.