What is Lynch syndrome—hereditary nonpolyposis colorectal cancer?

• Lynch syndromeis a condition that significantly increases colorectal (large bowel) cancer risk and is hereditary in nature.
• "Hereditary nonpolyposis colorectal cancer" (Hereditary Nonpolyposis Colorectal Cancer = HNCC) is another name for it.
• It is the most common cause of hereditary colorectal cancers.
• It accounts for % 3 – 5 of colorectal cancers.

How does Lynch syndrome develop?

Lynch syndrome is an autosomal dominant hereditary condition. In other words, it results from damage in chromosomes other than the sex-determining chromosomes. Individuals with a damaged gene have a high risk of developing cancer. However, not everyone carrying damaged Lynch-syndrome-associated genes develops cancer.

How is Lynch syndrome diagnosed?

Among carriers, the average age at colon cancer diagnosis is 44, and tumors are often located in the right colon (2/3). Lynch syndrome involves mutations in certain DNA repair genes, preventing repair of DNA damage and allowing damage to accumulate and lead to cancer.

The genes damaged in Lynch syndrome are MLH1, MSH2, MSH6, PMS2. Advanced genetic analyses identify damage in these genes to calculate the individual’s cancer risk.

When should Lynch syndrome be suspected?

• If someone was diagnosed with colorectal cancer at an early age (50 or younger) and
• Their family has more than 2 colorectal cancer cases across different generations, or
• Their family has more than 2 endometrial, stomach or ovarian cancer cases across different generations,

These individuals and their families should undergo genetic testing .

It must be emphasized that genetic test results help plan treatment and calculate cancer risk for other family members.