We don't know the exact cause of most colorectal cancers, but a great deal of research is being done in this area.
Researchers are beginning to understand how certain changes in DNA can cause normal cells to become cancerous. DNA is the chemical in each of our cells that makes up our genes -- the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. But DNA affects more than just how we look.
Some genes contain instructions for controlling when our cells grow, divide, and die. Certain genes that speed up cell division or help cells to live longer are called oncogenes. Others that slow down cell division, or cause cells to die at the right time, are called tumor suppressor genes. Cancers can be caused by DNA mutations (defects) that turn on oncogenes or turn off tumor suppressor genes. Mutations in several different genes seem to be needed to cause colorectal cancer.
Some DNA mutations may be passed from generation to generation and are found in all cells in the body. When this happens, we say the mutations are inherited. Other mutations happen during a person's lifetime and are not passed on. They affect only cells that come from the original mutated cell. These DNA changes are due to acquired mutations. These are the most common type of mutations. Some of the same genes are involved in both hereditary and acquired mutations.