Questions About Colon Cancer Genetics
Colon cancer is the second-leading cause of cancer death in the country and affects women and men in roughly equal numbers. One in 20 people, or about 5 percent, will be diagnosed with colon cancer. For women it’s the third-leading cause of cancer death after lung cancer and breast cancer.
The good news is that colon cancer is very preventable, unlike many other cancers, through appropriate screening. There is a variety of screening tests available, including colonoscopy, which, when applied at age 50 and repeated every 10 years, has the ability to reduce colon cancer deaths by roughly 50 to 90 percent.
When a person is diagnosed with colon cancer, a sample of the tumor can be evaluated to determine if the cancer is hereditary. If a patient is found to have hereditary colon cancer, this information can be passed along to other family members, which can save lives. Here, Dr. Terdiman provides more information about hereditary colon cancer and the lifesaving impact of genetic testing.1-2
What is hereditary colon cancer?
Hereditary colon cancer is colon cancer that develops as a result of an inherited genetic mutation. There are different types of hereditary colon cancer, but, in general, people who have hereditary colon cancer have a genetic change or mutation that puts them at an increased risk of colon cancer.
The most common type of hereditary colon cancer is Lynch syndrome, or hereditary nonpolyposis colorectal cancer (HNPCC). Five percent of colon cancers fall under Lynch syndrome; 1 in 300 to 400 people has the condition. In Lynch syndrome the risk of cancer is very high; lifetime risk is more than 50 percent, and cancers often occur at a younger age—many occurring before age 40 and even before age 30.
In addition, women with lynch syndrome have a 50 percent or higher risk of uterine cancer and a four- to five fold increased risk of ovarian cancer. Those with Lynch syndrome are also at higher risk of cancer of the liver, pancreas, skin, stomach, and urinary tract.
How do you know if you have hereditary colon cancer?
The tip-off for hereditary colon cancer is often family history of the disease but not always. Sometimes there can be a hereditary colon cancer without a striking or obvious family history because sometimes the first person in the family to have the hereditary colon cancer is the first person with cancer in the family—it starts somewhere—and nowadays families are small and people don’t always know family history.
Certainly, if there’s a family history of colon, uterine, or ovarian cancer, that’s a tip-off. But because family history is sometimes hidden and Lynch syndrome is so common, it should be considered in anyone diagnosed with colon cancer—especially if those cancers are occurring at a younger age, even if there is no family history.
We’ve realized that if we limit consideration of Lynch to patients who have a classic family history, we’re probably seeing only one-third to half of Lynch syndrome cases. Research studies have shown that every case of colon cancer should be evaluated for Lynch syndrome. Now many centers have adopted a universal testing approach so that every colon cancer case and every uterine cancer case is evaluated for Lynch syndrome. That approach is cost-effective and results in saving the most lives.
The reason why it is important to identify hereditary colon cancer is simple: when you identify someone who has had cancer and is a Lynch patient, you can go to all of the other members of that person’s family and figure out if they too have Lynch syndrome—that’s the key to saving lives.
If someone is found to have hereditary colon cancer, how will prevention or treatment be different for that person and any family members who are found to carry the genetic mutation?
When a patient is determined, through genetic testing, to have Lynch syndrome, other family members should be notified so that they can be tested to see if they also carry the mutation. This topic can be sensitive, but distributing this information can save lives. As a first step, seek the help of a genetics professional. Most hospitals have genetic counselors who are familiar with cancer genetics and can help patients navigate this process.
If a person who already has cancer is diagnosed with Lynch syndrome, there may be some different or additional treatment measures, so there is some benefit to the patient, but the bigger benefit is to all the relatives who don’t have cancer who benefit from increased screening.
If people who do not already have cancer are determined to have Lynch syndrome, they embark on increased prevention techniques and screening measures, which reduces the likelihood that they will get cancer.
Screening recommendations for someone diagnosed with Lynch syndrome include the following:
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Colonoscopy screening beginning at age 20 to 25 and continuing every one to two years. That reduces colon cancer mortality by 60 to 80 percent in those patients. Often with hereditary colon cancer, cancer occurs at a younger age, so if you wait to screen at age 50, that can be too late.
Daily aspirin. We now know that if people with Lynch syndrome take aspirin daily, it reduces the cancer rate by half—for all types of cancer associated with the mutation. We don’t recommend this for people at average risk.3-5
Regular uterine and ovarian cancer screening for women with Lynch syndrome starting at age 30. Some women also consider prophylactic surgery to prevent uterine and ovarian cancer; those techniques have also been proven to reduce cancer rates and death rates significantly.
Lynch Syndrome Is Associated With Other Cancers
Other cancers that are more common in families with Lynch Syndrome include cancers of the endometrium (the lining of the uterus), ovary, small intestine, ureter, and renal pelvis.
Small Intestine Cancer
According to the results of a study published in the journal Gut, the lifetime risk of small intestine cancer among individuals with Lynch Syndrome is roughly 4%.
To evaluate the lifetime risk of small intestine cancer among those with Lynch Syndrome, researchers in the Netherlands conducted a study among 1,496 individuals with a mismatch repair gene mutation.3 These individuals came from 189 different families.
- 28 cases of small intestine cancer were identified. Age at diagnosis of small intestine cancer ranged from 23 to 69 years, with a median age at diagnosis of 52 years.
- The lifetime risk of developing small intestine cancer was 4.2%. Risk was similar among men and women and did not vary significantly by history of colorectal cancer or family history of small intestine cancer.
- Information about presenting symptoms was available for 16 of the 28 patients with small intestine cancer. In nine cases, the patient presented with unexplained anemia. Six patients presented with small bowel obstruction and five patients reported abdominal pain. Jaundice, gastrointestinal bleeding, and weight loss were each reported by one patient.
This study suggests that roughly one out of 25 individuals with Lynch Syndrome will develop small intestine cancer during their lifetime. The researchers conclude that this risk may be too low to warrant routine use of invasive screening tests for small intestine cancer, such as double balloon enteroscopy.
Because the risk of small intestine cancer is higher among individuals with Lynch Syndrome than among the general population, however, the researchers note that small intestine cancer should be considered among individuals with Lynch Syndrome who experience unexplained abdominal complaints and/or unexplained iron-deficiency anemia.
Lynch Syndrome Increases Risk of Pancreatic Cancer
Lynch Syndrome, an inherited cause of colorectal cancer that also increases the risk of several other types of cancer, results in a risk of pancreatic cancer that is several times higher than the risk in the general population. These results were published in the Journal of the American Medical Association.
Pancreatic cancer may also be more common in families with Lynch Syndrome, but the risk has been uncertain. To explore the frequency of pancreatic cancer in families with Lynch Syndrome, researchers evaluated information from 6,342 individuals from 147 families with Lynch Syndrome.
- 21% of the families reported at least one case of pancreatic cancer.
- The risk of pancreatic cancer in families with Lynch Syndrome was 1.31% by the age of 50 and 3.68% by the age of 70. This risk is more than eight times higher than the risk in the general U.S. population.
The results of this study confirm that Lynch Syndrome is linked with an increased risk of pancreatic cancer and provide estimates regarding the lifetime risk of pancreatic cancer among affected family members.
- Kastrinos F, Mukherjee B, Tayob N et al. Risk of pancreatic cancer in families with Lynch Syndrome. Journal of the American Medical Association. 2009;302:1790-1795.
- Kate GL, Kleibeuker JH, Nagengast FM et al. Is surveillance of the small bowel indicated for Lynch Syndrome families. Gut. 2007;56:1198-1201.
- Burn J, Gerdes AM, Mecklin JP, et al. Aspirin prevents cancer in Lynch syndrome. European Journal of Cancer Supplements, Vol. 7, No. 3, September 2009. Abstract O-6000.
- Jacobs E, Thun M, Bain E, et al. A large cohort study of long-term daily use of adult-strength aspirin and cancer incidence. Journal of the National Cancer Institute. 2007; 99: 608-615.
- Burn J, Bishop T, Mecklin JP, et al. Effect of aspirin or resistant starch on colorectal neoplasia in the lynch syndrome. New EnglandJournal of Medicine. 2008; 359: 2567-2578.