MPA tumors harbor proportionally more C∶G→T∶A (at either CpG or CpNpG sites) transition mutations than MA tumors, showing recurrence in certain arginine codons, one of which was at Apc codon 854, a SBR hotspot that was also previously seen in Mlh1−/−;Apc1638N mice. Here, MLH1 is linked to microtia.