KRAS and colorectal cancer: Out of the 31 significantly mutated genes (excluding TTN) defined by The Cancer Genome Atlas (TCGA) colorectal cancer study [24], we found two mutations in KRAS and TP53 by bulk-cell DNA sequencing in our model (Fig. 1B), though the KRAS mutation was located outside of, but close (9 bps) to, an exon and the position was evolutionary conserved as much as exons (Additional file 1: Figure S1).