There does not seem to be a single pathway to colorectal cancer that is the same in all cases.
In many cases, the first mutation occurs in the APC gene. This leads to an increased growth
of colorectal cells because of the loss of this "brake" on cell growth. Further mutations may
then occur in genes such as KRAS, TP53, and SMAD4. These changes can lead the cells to
grow and spread uncontrollably. Other genes that aren't known yet are likely involved as
well.