Lynch syndrome is inherited in an autosomal dominant manner. It is sometimes referred to as a "cancer syndrome."
Lynch syndrome is associated with the instability of short tandem DNA repeats (micro-satellites) due to germ-line mutations in DNA mismatch repair genes (e.g., MLH1, MSH2, and MSH6). DNA mismatch repair is a mechanism for recognizing and repairing erroneous DNA base insertion during replication or tissue damage. This is a type of "cancer syndrome" leading to a predisposition for tumor formation.
There is a reported 80% incidence of colon cancer development in patients with Lynch syndrome.
Colorectal cancers from Lynch syndrome almost always involve the proximal, or right, colon. Lynch Syndrome I (HNPCC I) only involves the right colon, while Lynch Syndrome II (HNPCC II) involves the right colon along with other manifestations (endometrium, ovaries, skin).
Lynch Syndrome II (HNPCC II) involves the right colon along with other manifestations (typically endometrium, ovaries, or skin). Patients who are tested to have this genetic variation should be tested for carcinoma of the ovary, endometrium, small bowel, stomach, and pancreas.
The first part of the 3-2-1 rule, or Amsterdam criteria, is that there is a high suspicion of Lynch syndrome if the patient has 3 relatives with colon cancer.
The second part of the 3-2-1 rule, or Amsterdam criteria, is there is a high suspicion of this syndrome if the patient's relatives who have colon cancer show it occuring across two generations.
The third part of the 3-2-1 rule, or Amsterdam criteria, is that there is a high suspicion of Lynch syndrome if the patient one relative who was diagnosed with colon cancer under the age of 50 years old.
After meeting the 3-2-1 criteria, genetic screening is done to confirm the existence of Lynch syndrome. Once diagnosed with Lynch syndrome, frequent screening is important to prevent progressed, untreated colon cancer. Patients should have a colonoscopy every 6 months after reaching the age of 25 years old. Females will need regular endometrial and ovarian screening.
Surgery is the mainstay of treatment. Colectomy can be done electively to prevent cancer formation, or after tumors are found.
There is controversy about medical treatment, but aspirin has been studied in preventing colorectal cancer presentation in these patients.
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