Hereditary Nonpolyposis Colorectal Cancer

• HNPCC, also known as Lynch syndrome, is an inherited genetic disorder increasing cancer risk.
• It is caused by mutations in mismatch repair (MMR) genes, leading to DNA repair deficiencies.
• Individuals with HNPCC have a significantly higher lifetime risk of colorectal and other cancers, often at younger ages.
• Early screening, including regular colonoscopies, is vital for early detection and improved outcomes.
• Genetic testing is available to identify individuals and families at risk.

What is Hereditary Nonpolyposis Colorectal Cancer?

Hereditary Nonpolyposis Colorectal Cancer (HNPCC) is a genetic disorder that predisposes individuals to a higher risk of developing certain cancers, particularly colorectal cancer. Unlike familial adenomatous polyposis (FAP), another inherited colorectal cancer syndrome, HNPCC is characterized by the development of colorectal cancer without the presence of hundreds or thousands of polyps. This condition is now more commonly referred to as Lynch syndrome, reflecting its primary clinical manifestation. It is estimated that Lynch syndrome accounts for approximately 3-5% of all colorectal cancer cases, according to major health organizations, making it the most common form of what is hereditary colorectal cancer. The hallmark of HNPCC is its autosomal dominant inheritance pattern, meaning that a person only needs to inherit one copy of a mutated gene to be at increased risk.

Inherited Causes and Genetic Risk of HNPCC

The primary inherited colon cancer causes in HNPCC are germline mutations in specific genes responsible for DNA mismatch repair (MMR). These genes normally correct errors that occur during DNA replication, ensuring genetic stability. When one of these MMR genes is mutated, the cell’s ability to repair DNA is compromised, leading to an accumulation of genetic errors and an increased genetic risk for colorectal cancer and other malignancies. The most commonly affected genes include MLH1, MSH2, MSH6, and PMS2, along with EPCAM, which can lead to MSH2 inactivation. Individuals inheriting one mutated copy of an MMR gene have a significantly elevated lifetime risk of developing cancer, often at a younger age than in the general population. The specific gene mutation can influence the spectrum and age of onset of associated cancers.

• MLH1: Most common cause of Lynch syndrome, often associated with higher cancer risks.
• MSH2: Second most common, also linked to high cancer risks, including extracolonic cancers.
• MSH6: Associated with a later age of onset for colorectal cancer and a higher risk of endometrial cancer.
• PMS2: Generally associated with lower cancer risks compared to MLH1 and MSH2.
• EPCAM: Deletions in this gene can silence MSH2, leading to similar risks as MSH2 mutations.

Lynch Syndrome Symptoms and Screening

Individuals with Lynch syndrome typically do not present with specific Lynch syndrome symptoms that are unique to the condition itself, but rather experience cancer at an earlier age or develop multiple primary cancers. The most common cancer associated with Lynch syndrome is colorectal cancer, often diagnosed before age 50. Other cancers frequently seen in individuals with Lynch syndrome include endometrial (uterine), ovarian, stomach, small bowel, hepatobiliary tract, urinary tract, brain, and sebaceous gland tumors. Due to the significantly increased cancer risk, rigorous screening protocols are essential. For colorectal cancer, this typically involves colonoscopies every 1-2 years, starting between ages 20-25, or 2-5 years prior to the earliest age of colorectal cancer diagnosis in the family, whichever comes first. Screening for other associated cancers, such as endometrial cancer, may include annual transvaginal ultrasound and endometrial biopsy, especially for women approaching or past menopause. Genetic counseling and testing are crucial for individuals with a family history suggestive of Lynch syndrome to confirm the diagnosis and guide personalized screening and management strategies.