Four major types of gene mutations can lead to colorectal cancer. First, mutations in oncogenes, which help to control cell division, can lead to uncontrolled cell division and tumor formation. Second, mutations in the tumor suppressor genes that counteract uncontrolled cell division, which can result in cancer, cause them to lose this important function. People with polyposis have inherited a mutated tumor suppressor gene called the APC gene. Third, mutations in mismatch repair genes, which act to repair mistakes that occur in the formation of the genetic material, DNA, result in mistakes that can lead to cancer. People with the Lynch syndrome have inherited an abnormal mismatch repair gene. Fourth, more subtle gene changes, known as polymorphisms, are found in people with familial colorectal cancer.