Fig. 2: Different mutagenic mechanisms of platinum-based drugs and 5FU.

a Proportion of samples from metastatic tumors with different organs of origin taken from donors exposed to platinum-based drugs or 5FU with detectable treatment mutations. b Proportion of samples with detectable treatment mutations among distant or proximal metastases. c Platinum-based drugs and 5FU contribute mutations in the DNA via two different mechanisms (illustrated by the blue cells in the left panel). While the former creates adducts on the DNA, the latter alters the pool of nucleotides available for DNA replication. Thus, cells exposed to platinum-based drugs will carry mutations of the treatment after DNA replication, irrespective of whether cells are quiescent at the time of exposure or not (top arrow). On the other hand, 5FU-exposed cells will only incorporate mutations if their DNA is replicated while the pool of nucleotides is still distorted by the drug (middle arrow). If it has been restored before DNA replication, no mutations will be incorporated (bottom arrow). Therefore, immediately following exposure, two scenarios are possible: the surviving cells either bear treatment mutations (yellow cell) or not (blue cell). We reasoned that whether the treatment mutations are visible at the time of metastasis depends on the strength of the evolutionary bottleneck facing the primary tumor and its timing with respect to the exposure (see periods of time represented in different colors below figure). A stronger bottleneck during or immediately after treatment will lead to treatment mutations detectable through bulk sequencing (top drawing). On the contrary, a weaker bottleneck, or a bottleneck suffered before treatment (for example, if the metastasis predates the treatment) will lead to treatment mutations below the limit of detection of the bulk sequencing (middle drawing). d Distribution of time of treatment (days) and time after treatment (days) of samples of metastatic tumors of different organs of origin with detectable or undetectable treatment mutations taken from patients exposed to platinum-based drugs or 5FU. Groups of metastatic tumors were compared using a one-tailed Mann–Whitney test. The box in each boxplot delimits the first and third quartiles of the distribution (with a line representing the median); the whiskers delimit the lowest data point above the first quartile minus 1.5 times the interquartile distance and the highest data point below the third quartile plus 1.5 times the interquartile distance. e Results of logistic regressions showing the influence of different variables on the detection of platinum-based drugs (bottom) or 5FU (top) related mutations across metastatic tumors. Variables that significantly influenced the likelihood of detection are circled. BRCA breast adenocarcinoma, OV ovarian adenocarcinoma, UT urinary tract tumors, CR colorectal adenocarcinoma, 5-FU 5-fluorouracil.