Lynch Syndrome is also known as hereditary non-polyposis colorectal cancer. It is the most common cause of inherited colorectal cancer accounting for 3% of all newly diagnosed cases of colorectal cancer and 3% of endometrial cancer. Colorectal cancer is the 2nd leading cause of cancer-related death in the United States.
Lynch Syndrome refers to patients and families with a genetic mutation in one of the DNA mismatch repair (MMR) genes. It is seen in approximately 1 in 279 people in the population. As we age, errors in DNA replication tend to occur more frequently resulting in abnormal genes being produced which produce abnormal function in the body. The role of the DNA mismatch repair system is to maintain correct DNA base pairs and prevent abnormal gene expression that leads to conditions such as cancer. Microsatellite Instability (MSI) is when regions of repetitive DNA sequences fail to be repaired correctly. This is a characteristic of tumors in Lynch Syndrome. However, 15% of sporadic (non-inherited) colorectal cancers demonstrate MSI.
The major clinical manifestation of Lynch Syndrome is colorectal cancer (CRC). Patients with this condition may be asymptomatic or may have worrisome symptoms such as abdominal pain, blood in their stool, or a change in the pattern of their bowel habits. The lifetime risk of colorectal cancer for Lynch Syndrome varies but can be as high as 47%. Colorectal cancer in Lynch syndrome tends to occur at a younger age (45-60 years) compared to sporadic colon cancer (69 years). Patients with Lynch Syndrome are at risk for more than one location of colon cancer developing at the same time (synchronous) and developing colon cancer again after the initial cancer is found and treated (metachronous). Seven percent of patients have more than one cancer at the time of diagnosis. The cancers that develop in Lynch Syndrome tend to occur in a different location in the colon compared to sporadic CRC, the right side of the colon also known as the proximal colon. These polyps tend to be large, flat and more aggressive. In Lynch Syndrome, the time it takes a polyp to develop into cancer is relatively short (35 months) compared to sporadic CRC (10-15 years).
Other Cancer Types Associated with Lynch Syndrome
Lynch Syndrome is also associated with diseases outside of the colon; the most common is endometrial (uterine) cancer. Other cancers that are associated with Lynch Syndrome include ovarian, stomach, small bowel, bile duct, ureter, brain (gliomas) and sweat gland tumors (sebaceous neoplasms). A rare condition called Muir-Torre syndrome is a variant of Lynch Syndrome and is characterized by sebaceous tumors.
Lynch Syndrome Diagnosis
The diagnosis of Lynch Syndrome can be challenging and is therefore often overlooked. Different strategies for identifying individuals at risk for the condition consider family history, prediction models, tumor-based testing (which includes MSI testing), and genetic analysis. The Amsterdam I criteria are frequently used and can be simplified by using the “3-2-1 rule.” Patients at risk for Lynch Syndrome will have 3 or more relatives with Lynch Syndrome-related cancers including a first degree relative, 2 generations are affected by Lynch Syndrome related cancers, and 1 or more cancers were diagnosed before age 50 years. Other systems have been proposed for identifying patients at risk; one is known as the Bethesda guidelines.
Lynch Syndrome should be suspected when a patient meets certain criteria. Those criteria include identifying more than one CRC at the time of diagnosis, identifying a second CRC in the same individual over time, diagnosing CRC at an age less than 50 years, or identifying multiple Lynch Syndrome-related cancers (see above). In order to reach a definitive diagnosis of Lynch Syndrome, an abnormal genetic mutation in the mismatch repair gene (MMR) must be identified.
Individuals who may be candidates for genetic testing include the following:
– All newly diagnosed CRC
– Endometrial (uterine) cancer diagnosed before age 60 years
– First degree relative with known MMR/EPCAM genetic mutation
– Newly diagnosed CRC and an elevated risk based on prediction models
– Family history meeting above Amsterdam-type criteria
This overview of the Lynch Syndrome focuses on what defines the syndrome and who should be considered for additional testing. In future installments, the specific tests to be ordered and frequency of testing will be reviewed.
If you have questions about your GI health or how hereditary gastrointestinal conditions may play a part in your overall health picture, contact the gastroenterologists at Granite Peaks Gastroenterology for answers.