What Causes Colon Cancer?

What causes colon cancer, and how can screening and lifestyle choices reduce your risk?

Colorectal (colon and rectal cancer) is a leading cause of cancer death in the U.S., impacting both men and women. In men, the lifetime risk of developing colorectal cancer is about one in 24; in women, it’s about one in 26.

While the incidence of colon cancer has fallen annually among older adults since the mid-1980s, due in part to increased awareness and screening, rates of colon cancer have increased in people under 50.

Colon cancer develops gradually over many years through a series of changes in the DNA of cells lining the intestine, explains Syma Iqbal, MD, section chief of gastrointestinal oncology with the USC Norris Comprehensive Cancer Center, part of Keck Medicine of USC. These abnormal cells multiply and can eventually develop into cancer. Your immune system normally identifies abnormal cells, such as cancer, but cancer cells develop ways to evade detection.

Abnormal cells often manifest as polyps — small, noncancerous growths on the colon lining — called adenomas. “If left alone, a small percentage of them can eventually turn into cancer,” Dr. Iqbal says.

Major risk factors for colon cancer

According to Dr. Iqbal, colon cancer risk factors fall into several categories.

Genetics and family history: Only about 15% of colon cancers stem from inherited genetic syndromes. Having a first-degree relative who had colon cancer, such as a parent or a sibling, however, may still increase your risk of developing colon cancer.

Lifestyle factors: Most colorectal cancers are “sporadic,” meaning that random genetic mutations, lifestyle factors and environment play a significant role in their development, Dr. Iqbal says. These factors may be especially significant for younger adults, among whom colon cancer rates are increasing. Lifestyle factors that may contribute to colorectal cancer risk include certain processed foods; red meat and alcohol can increase your risk of developing colon cancer. Those who are sedentary or overweight may also be at higher risk. Conversely, maintaining regular exercise and a healthy weight may be protective against colorectal cancer. And, finally, low levels of vitamin D are associated with increased risk, particularly in young people.

Medical conditions: Inflammatory bowel diseases, especially ulcerative colitis, and diabetes are two conditions linked to a higher risk of developing colorectal cancer.

In addition, it has been shown that early-onset colorectal cancer occurs at higher rates in Hispanic and Black populations.

How to prevent colorectal cancer

Screening is crucial for detecting colorectal cancer early. Colonoscopy is the gold-standard screening method because, as Dr. Iqbal indicates, “With direct visualization, we can actually see these polyps, then remove them,” preventing potential cancer progression. Current screening guidelines recommend:

• Average-risk individuals: Begin at age 45 and then screen every 10 years.
• If you have a first-degree relative with colon cancer: Begin screening 10 years before the age at which your relative was diagnosed with colon cancer, or begin screening at age 45, whichever comes sooner. For instance, if your brother was diagnosed with colon cancer at age 40, you should start screening at age 30. But if your mom was diagnosed at age 60, then you would start screening at age 45.
• Genetic syndromes or inflammatory bowel diseases: People in this category should follow the specific guidelines of a gastroenterologist.

Dismissing symptoms can delay crucial diagnosis. Pay attention to any persistent changes in your body, as early detection dramatically improves treatment outcomes. Be aware of potential warning signs and seek medical attention for persistent changes such as blood in stool, changes in bowel habits or unexplained pain or weight loss, Dr. Iqbal says. Address modifiable risk factors through diet, exercise and maintaining a healthy weight.

The earlier detection and treatment starts, the more promising outcomes will be. Dr. Iqbal emphasizes that physicians can cure a large majority of colon cancer patients these days, even for many whose cancer has spread. Take heart knowing that detection and treatment options continue to advance.

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