KRAS and cancer: No significant difference was detected comparing cancer-bearing (adenoma or adenocarcinoma) and cancer-free mice in either percentage of KRAS mutations (11.0 ± 2.1 vs. 11.6 ± 2.0), let-7a expression (0.030 ± 0.001 vs. 0.029 ± 0.001), or let-7a promoter methylation (52.5 ± 4.4 vs. 51.0 ± 6.3).