But researchers do know that colorectal cancer is a result of damage to a cell’s DNA, resulting in genetic changes called mutations. A small percentage of mutations capable of causing colorectal cancer are inherited, meaning passed along in families. Most, however, are acquired, meaning they develop during a person’s life, generally because of environmental or lifestyle factors. For the majority of people who develop colorectal cancer, there’s no single genetic pathway to disease. Scientists are working to better understand the complex interplay of factors that cause this cancer.
Inherited Causes of Colon Cancer
A small number of people will inherit genetic mutations from their families that dramatically raise their risk for colorectal cancer. They generally develop certain syndromes (sets of symptoms) connected with this genetic legacy. These include:
Familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and Gardner syndrome These conditions relate directly to the inheritance of a mutated APC gene. When functioning properly, APC serves as a brake on cell growth. When mutated, it becomes part of a biochemical chain reaction that leads to the formation of hundreds of polyps in the colon that can become cancerous. Lynch syndrome (hereditary non-polyposis colon cancer, or HNPCC) This is an inherited cancer syndrome that raises the risk for many cancers, including colorectal cancer. Mutations generally occur in the MLH1, MSH2, MSH6, PMS2 or EPCAM genes. These genes are involved in DNA repair. When they’re mutated, they are not able to prevent mutations that can lead to cancer. Peutz–Jeghers syndrome Mutations in the STK11 gene (also referred to as LKB1) cause most cases of this syndrome. When not mutated, the gene prevents cells from growing in a rapid and uncontrolled manner. Uncontrolled growth, in this case, leads to colorectal polyps that can become cancerous. MYH-associated polyposis (MAP) Mutations in the MYH gene play a role in how cells identify and correct DNA errors made during cell division which also contribute to cancer. (1)
RELATED: Lynch Syndrome: Knowing Your Cancer Risk Could Save Your Life
Colon Cancer Risk Factors You Can’t Control
Some colon cancer risk factors are not under your control. This list includes: Age While there are a growing number of people being diagnosed with early-onset colorectal cancer, the majority of people with the disease are older than 50. Personal or family history If you have had colorectal polyps (abnormal growths in the colon or rectum), you are more likely to develop colorectal cancer. This is especially true if the polyps are big, appear in multiples, or contain cells with noncancerous abnormalities (dysplasia). A family history of colorectal cancer is another risk factor. One out of three people diagnosed with colon cancer or rectal cancer have family members with the disease. Having had colorectal cancer makes you more likely to get it again, even if you were successfully treated the first time. A personal history of inflammatory bowel disease (IBD) Inflammatory bowel disease, which includes Crohn’s disease and ulcerative colitis, causes chronic inflammation of the colon. This can lead to dysplasia, which may eventually become cancer. African-American or Eastern European Jewish heritage African-Americans have one of the highest rates of colorectal cancer of any racial group. The American College of Gastroenterology suggests that African-Americans begin colorectal screening at age 45, five years earlier than non–African-Americans at average risk. (2) Jews of Eastern European descent, called Ashkenazi Jews, are also at high risk compared with other ethnic groups. Type 2 diabetes People with this form of non-insulin-dependent diabetes not only face a higher risk of colon cancer and rectal cancer, they tend to have a less favorable prognosis after diagnosis. (3)
Risk Factors Under Your Control
There are some colorectal cancer risk factors that you can modify (at least theoretically). They include: Being overweight Men and women who are overweight or obese face an increased risk of colorectal cancer. Men, especially those who amass extra pounds around their midsection, are the most vulnerable. Increasing rates of colorectal cancer among younger people may also be due to rising obesity rates. A study published in JAMA Oncology in 2018 tracked the health of more than 85,000 women for 22 years and found that the higher a woman’s body mass index (BMI), the greater her risk of developing colorectal cancer before age 50. The study found that women ages 20 to 49 who were considered overweight or obese had up to twice the risk of developing early-onset colorectal cancer as women who reported the lowest BMIs. (4) Being sedentary There’s a solid body of evidence connecting a sedentary lifestyle with an increase in colorectal cancer risk and rectal cancer risk. A meta-analysis of 28 research studies, published in the journal Medicine in 2017, found a statistically significant association between daily sedentary time — specifically, TV watching — and colorectal cancer risk. The study also found that people who had jobs that required prolonged sitting were more likely to develop colorectal cancer. The researchers discovered that each two-hour increase in daily TV watching raised colorectal cancer risk by 7 percent; two additional hours of job-related sitting led to a 4 percent increase. (5) A meat-heavy diet A diet with a lot of red meat and processed meat (certain luncheon meats, hot dogs, sausages) has been associated with an increased risk of colorectal cancer. The International Agency for Research on Cancer, the cancer agency of the World Health Organization, has gone so far as to label processed meat a carcinogen and red meat a probable carcinogen. Twenty-two experts from 10 countries reviewed more than 800 studies to reach these conclusions. They found that eating 50 grams of processed meat every day — the equivalent of about four strips of bacon or one hot dog — increased the risk of colorectal cancer by 18 percent. (6) Drinking alcohol to excess Researchers have found an association between moderate to heavy alcohol use and higher risk of cancers of the colon and rectum. Evidence for this is generally stronger for men than women, but studies have found a connection for both sexes. Smoking Most people know that smoking raises lung-cancer risk, but there’s less awareness that it also increases colorectal cancer risk.
