Analogous to cancer mutations that perturb ARF function32,33, exome signals in the Cdkn2a gene, which encodes ARF, were almost completely absent after IP1 in Msh2−/− MEFs (Fig. 4a), suggesting that this locus was deleted during P8–IP1 when cells were subjected to replication stress and MSI was induced. This evidence concerns the gene MSH2 and cancer.