A statistical analysis of the base substitution patterns is shown in S5 Table. Among the filtered variants, 23.3% were G>T/C>A transversions and 62.8% were C>T/G>A transitions. Among the variants removed by the CV78 filter, 32.2% were G>T/C>A transversions and 40.6% were C>T/G>A transitions. These transversions and transitions were the major mutations detected in both data sets. Their dominance among the filtered variants suggests that tumor-specific mutations likely arise via oxidation/deamination and are repaired by cell proliferation.