APC and neoplasm: A heterozygous C→T transition within APC not previously identified as a naturally occurring polymorphism or reported in the COSMIC mutation database (20) and predicted to create a premature termination codon in the APC coding sequence at position 861 was consistently observed in 62–82% of the reads from all samples in the D61540 tumor lineage, including the two halves of the parental tumor as well as its first- and second-generation xenografts (Table 2).