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HNPCC (hereditary nonpolyposis colorectal cancer)

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was reviewed on August 29, 2022.

The most common cause of inherited colon cancer is Lynch syndrome, also called hereditary nonpolyposis colorectal cancer (HNPCC).

HNPCC may also increase the risk of developing other cancers at an earlier age, including ovarian, endometrial, esophageal, stomach, liver, kidney, small intestine, urinary tract, prostate, brain, and skin cancers.

HNPCC is responsible for about 4,200 colorectal cancers and 1,800 endometrial cancers each year, according to the Centers for Disease Control and Prevention, and accounts for 2 to 4 percent of all colorectal cancers according to the American Cancer Society. People who develop cancer because of Lynch Syndrome are usually in their 40s or 50s.

Polyposis vs. nonpolyposis

Another yet rarer form of inherited colon cancer causes hundreds or thousands of polyps or precancerous growths in the colon (“polyposis”). The most common type is called familial adenomatous polyposis (FAP). The polyps may start to develop during a person’s teenage years. If FAP is not addressed—typically with surgical intervention—it may result in colon and/or rectal cancer at a young age. One or more of these polyps may become cancerous by as early as age 20.

By contrast, people with Lynch syndrome, or the nonpolyposis colorectal cancer, usually develop one or a few polyps in their colon at a young age, instead of the hundreds or thousands that can be caused by FAP.

FAP is caused by mutations in the APC gene that a person inherits from their parents. FAP is responsible for about 1 percent of all colorectal cancers, according to the American Cancer Society. People with FAP also have an increased risk for stomach, small intestine, pancreatic, liver, and some other types of cancer. The lifetime risk of developing colorectal cancer for people with FAP is nearly 100 percent, according to the American Cancer Society and in most cases develops before the age of 50.

There are several types of FAP:

Attenuated FAP: This is characterized by an increased risk for colorectal cancer that’s lower than what is seen with classic FAP. People with this type of FAP have fewer polyps that tend to occur later in life than those with classic FAP.

Gardner syndrome: This is a type of FAP that also causes noncancerous tumors of the skin, soft tissue and bones.

Turcot syndrome: This is a rare inherited condition characterized by the formation of multiple benign growths (polyps) in the colon that occur in association with a primary brain tumor.

How is HNPCC inherited?

Several genetic mutations may increase the risk for Lynch syndrome, namely those that occur in the MLH1, MSH2, MSH6 or PMS2 genes. Changes in other genes may also cause Lynch syndrome. The lifetime risk of colorectal cancer in people with Lynch syndrome may be as high as 50 percent, depending on which gene is affected, according to the American Cancer Society. Lynch syndrome cancer risk is inherited via an autosomal dominant pattern. This means that a person only needs to get the abnormal gene from one parent to develop the disease.

HNPCC screening

If a family member is diagnosed with colorectal cancer, the treating doctor will typically order screening to see if the cancer is caused by Lynch syndrome. This may be done using a blood or saliva test. A genetic counselor may be called in to help process the results.

This information may also serve as a call to action for close family members. It means that close relatives have a chance of having a mutation too and may want to be tested or start screening for certain cancers earlier than would otherwise be recommended.

For these people, experts such as those with the U.S. Centers for Disease Control and Prevention generally recommend undergoing colonoscopies every one to two years starting between the ages of 20 and 25, or two to five years before the earliest colorectal cancer was diagnosed in the family. This may help loved ones get ahead of colon cancer.

Lynch syndrome also increases risk for other cancers, including esophageal or upper gastrointestinal cancer. Patients with Lynch syndrome should consider undergoing upper endoscopy every three to five years along with testing for Helicobacter pylori (H. pylori) infection at a baseline exam with treatment if positive.

Other screening options may include:

  • Total body skin examination to look for skin cancer every one to two years
  • Urinalysis every year starting between the ages of 30 and 35 to detect bladder cancer
  • Early prostate cancer screening for men, starting at age 40
  • Yearly pelvic exams, pelvic ultrasound and/or endometrial biopsy for women starting at age 30 to 35, due to increased risk for endometrial cancer with Lynch syndrome

HNPCC symptoms

Patients with Lynch syndrome develop benign polyps in their colon, and these occur at younger ages than they would in patients without this genetic syndrome.

The revised Bethesda guidelines help doctors decide who should be screened for Lynch syndrome. The list includes:

  • People who developed colorectal or endometrial cancer before they turned 50
  • People with certain genetic defects found after testing a sample of the tumor
  • Individuals who develop colorectal cancer and other types of cancer linked with Lynch syndrome separately or at the same time
  • People with one or more first-degree relatives who had colorectal cancer or another Lynch syndrome-related cancer, with one of these cancers developing before age 50

HNPCC treatment

Lynch syndrome treatment involves hypervigilance when it comes to screening to catch and remove polyps before they have a chance to become cancerous. If a patient with Lynch syndrome does develop colon or another related cancer, treatment is the same as it would be for an individual with the cancer who doesn’t have this genetic condition.

Women with Lynch syndrome may consider removal of the uterus and both fallopian tubes and ovaries (hysterectomy and bilateral salpingo-oophorectomy) to prevent uterine and ovarian cancer. It should be noted that this option will permanently remove the ability to get pregnant, so this should be carefully considered before making a decision.

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