How often have you heard this? “My father had colon cancer.” “My mother’s father had rectal cancer.” “My sister had rectal cancer and my father had colon polyps.”
Colorectal cancer is a common malady in the United States and indeed in the world. It accounts for approximately 150,000 new cancer cases per year. Approximately 50,000 Americans die each year from colorectal cancer. And yet, it is preventable. Polyps are harmless overgrowths of the tissue lining the colon or rectum. Colon cancer screening, examining the colon and rectum for the presence of these polyps, allows a physician to remove the polyps before they can transform into a colon or rectal cancer. Colonoscopy and polypectomy, the optical evaluation of the colon and rectum with the removal of polyps, saves lives.
IS IT IN MY GENES?
Colorectal cancer is common. Equally common are erroneous statements as to how colorectal cancer develops and the role that hereditary and genetics may play in the development of this disease. In fact however, hereditary colorectal cancer accounts for less than 5% of all new cases of colorectal cancer each year. Most colorectal cancer is actually sporadic, meaning that it is randomly distributed throughout the population and has no discoverable cause.
While genetics plays a role in every cancer, and while it is our genes that both facilitate the development of cancer and may even stop the advance of cancer, very few of the new cases of colorectal cancer each year begin because of a hereditary genetic component.
WHAT KINDS OF HEREDITARY COLORECTAL CANCERS ARE COMMON?
There are many hereditary colorectal cancers, but only two of these are relatively common. These are Hereditary Nonpolyposis Colorectal Cancer (HNPCC), and Familial Adenomatous Polyposis, or FAP.
FAP is a disease whereby the body loses its ability to control the development of colorectal polyps. If left unchecked, these polyps can develop into a cancer. Patients with FAP develop hundreds, if not thousands of polyps and the incidence of colorectal cancer in patients with FAP is almost 100%. Researchers have identified a gene known as the APC gene which, when defective, or mutated, initiates the polyp to cancer sequence in thousands of polyps in the colon or rectum. If FAP is detected at an early stage, at a stage before a malignancy has developed, operative therapy can be curative.
Most often, patients with FAP inform their family members so that the family members can be tested for the abnormal APC gene, or can be screened using colonoscopy, in order to evaluate the colon lining. Early diagnosis can lead to a high cure rate.
HNPCC can be more insidious. Usually, it is diagnosed after an operation for colon cancer. When the tumor is tested in the laboratory using microscope techniques, the tumor may show certain features consistent with the hereditary component which caused the cancer in the first place. Under the microscopic, the tumors of HNPCC patients may look different compared with a tumor from a patient with sporadic colorectal cancer. If HNPCC is diagnosed, HNPCC testing can be performed on unaffected family members of the patient with HNPCC.
The genes responsible for the development of HNPCC are known as mismatch repair genes, or MMR genes. While there are many MMR genes, 6 of them cause the majority of inherited colorectal cancer, and HNPCC. MMR genes are responsible for making sure that when cells normally divide, the cellular division is accomplished correctly. When cells divide, the MMR genes look for and initiate repair of the newly divided genes and their DNA. DNA is the genetic material that controls all aspects of our bodily functioning. When MMR genes are absent or are defective, cell division may proceed unchecked and in a rapid fashion, leading to the development of abnormal cells with abnormal DNA. This often leads to the development of colorectal cancer.
Tests are available to evaluate patients whose families may be at high risk for the development of HNPCC. The tests involve testing a blood sample for the presence of mutant MMR genes. If detected, early and frequent colorectal polyp screening is initiated. Operations can be performed to prevent the development of cancer detected in its early stages.
WHAT SHOULD I DO?
Colorectal surgeons are trained in the genetics of colorectal cancer and are ideally suited to study, diagnose and treat patients and family members who have a suspected hereditary colon or rectal cancer.
By calling Lapeer Surgical Center, you can be referred to a physician who will be able to talk with you, examine you and guide you through what can be a confusing problem, hereditary colorectal cancer.