The 3/2:1 rule for colorectal cancer is also known as the 3-2-1 rule and is an Amsterdam Criteria that is used to identify families that are at high risk for Lynch syndrome, which requires 3 or more relatives with colorectal cancer or related cancers, 2+ generations that are affected and 1 or more relatives that are diagnosed before age 50.
The 3-2-1 rule for colorectal cancer helps to identify people with a need for genetic testing.
The key aspects and details of the 3-2-1 rule are that at least 3 relatives with histologically verified cancer, "colorectal cancer, endometrial cancer, small bowel cancer, renal pelvis cancer or ureter cancer.
At least 2 successive generations must also be affected.
And at least one cancer diagnosis must also occur before age 50, with one person being a first degree relative of the other two.
The 3-2-1 rule for colorectal cancer requires excluding a diagnosis of Familial Adenomatous Polyposis or FAP.
Also the 3-2-1 rule for colorectal cancer also specifically targets Lynch syndrome and is also used to identify families that should undergo genetic testing.
And if a family does meet these criteria, there is also a 50 percent to 70 percent chance that a genetic mutation for Lynch syndrome will be found in family members.
Lynch syndrome is an inherited genetic condition that significantly increases the lifetime risk of developing colorectal, endometrial, and various other cancers, often at a young age (before 50).
Lynch syndrome which is caused by mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2, EPCAM), is inherited in an autosomal dominant pattern.
And beyond colon cancer and uterine and endometrial cancer, risks are also increased for cancers of the ovary, stomach, small intestine, kidney, pancreas, brain, kidney, bile duct and skin.
And often no symptoms occur with Lynch syndrome until the cancer develops.
Potential symptoms of related cancers are unexplained anemia, blood in poop, abdominal pain and abdominal uterine bleeding.
A mutation in one of 5 mismatch repair genes prevents cells from fixing of DNA errors, which lead to cancer and a person with Lynch syndrome has a 50 percent chance of passing it on to their children.
And a strong family history of colon cancer or endometrial cancer, especially at young ages is the main risk factor for Lynch syndrome.