By comparing the mutation rate of the first event in the orders with KRAS − APC − TP53, APC − TP53 − KRAS and APC − KRAS − TP53, we find that the initiated rate in the order with KRAS − APC − TP53 is lower than that in other orders with high probability in initiation of colorectal cancer. The gene discussed is KRAS; the disease is colorectal cancer.