The American Cancer Society predicts that in 2021 there will be 104,270 new cases of colon cancer and 45,230 cases of rectal cancer. These numbers are high, yet fewer and fewer people are diagnosed with these cancers since the mid-1980s. Screening methods are more widespread, and the public is more aware of the lifestyle risk factors associated with colorectal cancer. A growing portion of the American population is striving to make the necessary changes in their lifestyle to reduce the risk of colon cancer and other diseases.
As is the case with most other types of cancer, there is no single, clear cause of colon and rectal cancers. Instead, many risk factors are associated with the onset of this disease. Some of these risk factors for colorectal cancer can be reduced or eliminated (variable), while others are harder, if not impossible to influence or adapt (fixed).
Here we outline both types of risk factors, fixed and variable. We focus on the stages of colon carcinogenesis and what you can do to help prevent this disease.
Lifestyle Risk Factors
- High-fat, low-fiber diet. Research results are mixed in this area. However, some studies have demonstrated that a typical Western diet high in fats and calories and low in fibers may be a risk factor for colorectal cancer. An increased risk for colon cancer is also observed in individuals with diets high in red and processed meats (such as hot dogs, luncheon meats, lamb, pork, beef, etc.).
- Obesity. According to one study, people with obesity are around 30% more likely to develop colorectal cancer than average-weight people. A higher BMI is linked to an increased risk of these cancers in both biological sexes, though the association appears to be more prevalent in males. The risk of cancer is higher the longer the duration of obesity is. Maintaining a healthy weight is vital for reducing the risk of cancer.
- Sedentary lifestyle. Sedentary behavior is one of the significant colorectal cancer risk factors. Furthermore, prolonged sedentary TV-viewing time (a stereotypical example of an inactive lifestyle) leads to an increase of young-onset colorectal cancer, particularly of the rectum. There is no “magic number” of hours that individuals should be watching TV or exercising, but everyone should strive for as much activity in their daily life as possible.
- Diabetes. The risk of colorectal cancer is estimated to be 27% higher in patients with type 2 diabetes mellitus than in non-diabetic individuals.
- Smoking. Smoking – especially prolonged smoking – may have an increased risk of colon cancer.
- Alcohol. Moderate to heavy use of alcohol increases colorectal cancer risk. Limiting your consumption of alcohol may also lead to lowering your risk of other types of cancers.
Fixed Risk Factors
- Older age. Colon cancer is prevalent among people older than 50 years. However, the disease is becoming more widespread among younger adults as well. As of 2019, one in five patients with colon cancer is between 20 and 54 years old. Doctors are still not sure why this increase of colorectal cancer among the relatively younger population is occurring – it is possibly related to the lifestyle risk factors outlined above.
- Race. African-Americans have a higher risk of colon cancer than members of other racial groups.
- Personal history of polyps or colorectal cancer. Your risk of developing colorectal cancer is higher if you’ve already had colon or rectal cancer or even non-cancerous colon polyps.
- Family history of colorectal cancer. If you have a blood relative who has been diagnosed with colorectal cancer, you are more likely to get it as well. The risk is greater if you have more than one blood relative with this diagnosis.
- Inflammatory bowel disease. Inflammatory intestinal conditions, such as Crohn’s disease or ulcerative colitis, increase colon cancer risk. Patients with these conditions have a colon that could be inflamed for an extended period. The inflammation can affect only one part of the colon, such as the transverse or the sigmoid colon, but it could also affect the entire colon. This prolonged inflammation could cause abnormal development of cells in the colon’s lining, which could potentially develop into cancer cells. It should be noted that inflammatory bowel disease is different from irritable bowel syndrome.
- Genetic mutation. A small percentage of colon cancer is associated with inherited gene mutations. Yet, genetic predisposition can significantly increase the risk of colon cancer. The most common inherited syndrome that leads to colorectal cancer is Lynch syndrome. It is also known as hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis syndrome (FAP). Genetic testing could reveal the presence of these mutations.
- Radiation treatment. If you have been treated with radiation therapy for some other form of cancer in the abdominal area, your risk of colorectal cancer increases.
The Development of Cancer
The telltale sign of the initial stages of colon cancer is polyps. A polyp is a growth in the inner lining of the colon or the rectum. It can be a noncancerous polyp that never becomes cancer, but it could also be a precancerous polyp that eventually (over many years) develops into cancer. Whether or not colorectal polyps become cancer depends on the type of the polyp.
- Adenomatous polyps (adenomas). Adenomas are considered precancerous polyps because they may be a precursor to colon or rectal cancer. Two major growth patterns of adenomas are observed: villous and tubular adenomas. Many adenomatous polyps have a combination of these two patterns and are thus considered tubulovillous adenomas. Larger adenomas tend to have a villous growth pattern and are more likely to develop cancerous cells.
- Hyperplastic polyps and inflammatory polyps. This is a common type of polyp, but it is considered benign (harmless, noncancerous). If a hyperplastic polyp grows to more than 1 cm, it might require more frequent colon cancer screening via colonoscopy.
- Sessile serrated polyps (SSP) and traditional serrated adenomas (TSA). SSP and TSA are considered precancerous polyps. They have a higher likelihood of developing into colon cancer and thus also require frequent screening.
If a polyp evolves into cancer, it continues growing into the colon or rectum tissue over time. Cancerous cells begin in the mucosa, the innermost layer of the bowel wall, and extend outward from there. They can permeate other layers of the lining and travel through blood vessels or lymph vessels (channels that transport fluid and waste). Once in the vessels, there is no telling where the cancer cells end up in the body. It can be in the nearby lymph nodes or other organs, or distant sites in the body. The extent to which colon cancer will spread depends on how much of the colon and rectum wall it has occupied and its spread outside of the digestive tract. Colorectal cancer cells that spread outside of the colon or rectum are called metastases.
What can you do to prevent colon cancer?
Regular colorectal cancer screening is the best preventive measure currently available. Everyone over the age of 45 with average risk should undergo colon cancer screening at least once a year. Early screening is recommended for those younger than 45 who have substantial risk factors, such as a personal or family history of this type of cancer. Screening can be performed as colonoscopy, X-ray testing, or fecal testing (testing based on stool samples, a minimally invasive procedure).
To prevent colon cancer development, try to reduce or eliminate the risk factors you can influence. Eat a balanced diet, introduce light to moderate amounts of activity in your daily life, and reduce alcohol and cigarette intake. This is especially important if you also have any fixed risk factors.
If a cluster of abnormal cells or a precancerous polyp exist, it usually takes them between 10 and 15 years to develop into colon cancer cells. Leading a healthy lifestyle and getting checked regularly for colorectal cancer are the cornerstones of prevention.
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