As many as 150,000 cases of colorectal (colon and/or rectal) cancer are diagnosed each year in both men and women of all ages. Five to ten percent of these cases are caused by inherited gene mutations that increase a person's lifetime risk of colorectal cancer. Hereditary nonpolyposis colorectal cancer (HNPCC) and the adenomatous polyposis syndromes are the most common inherited syndromes that increase the risk for colorectal cancer and, in some cases, for other cancers. The adenomatous polyposis syndromes include familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and MYH -associated polyposis (MAP).
The most distinct difference between the inherited colorectal cancer syndromes is the number of polyps that develop in the colon and rectum. The adenomatous polyposis syndromes are all associated with multiple precancerous (adenomatous) colorectal polyps. Usually patients with these conditions develop between ten and thousands of polyps throughout their lifetime. In contrast, HNPCC is associated with very few polyps that appear mostly on the right side of the colon. With all the inherited colorectal cancer syndromes, there is a significant lifetime risk of colorectal cancer.
HNPCC is caused by an inherited mutation in the MLH1, MSH2, or MSH6 genes that, when functioning normally, work to prevent cancer. Signs of HNPCC include early-onset (often before age 50) of colorectal and/or endometrial (uterine) cancer, as well as other related cancers such as: ovarian, stomach, kidney/urinary tract, brain, biliary tract, pancreas, small bowel, and sebaceous adenomas.
» Understanding Inherited Colorectal Cancer: HNPCC
There are three adenomatous polyposis syndromes: familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and MYH -associated polyposis (MAP). FAP is caused by an inherited mutation in the adenomatous polyposis coli (APC) gene that leads to the development of hundreds to thousands of precancerous (adenomatous) colon polyps. Attenuated FAP (AFAP) is a form of FAP but is characterized by fewer polyps (usually between ten and 99). Both FAP and AFAP also increase the risk of developing other cancers such as: small bowel, thyroid, pancreas, and brain. MAP is caused by an inherited mutation in the MYH gene. Patients with MAP may have many polyps and look similar to those with FAP. However, they may also present with a smaller number of polyps, as in AFAP.
It is important to note that not all patients with adenomatous polyposis syndromes will have a family history of colorectal polyps or cancer.
» Understanding Inherited Colorectal Cancer: Adenomatous Polyposis Syndromes
A genetic test for hereditary nonpolyposis
colorectal cancer (HNPCC)
A genetic test for adenomatous polyposis
syndromes
