Colon cancer: Can you reduce your risk? Here's what you need to know.
Colorectal cancer is the third most commonly diagnosed cancer in the world, and the second deadliest. It affects both men and women, mostly those who are aged 50 and older. However, cases among younger adults are increasing, with 20% of diagnoses in 2019 in patients under age 55.
Colon cancer accounts for around 10% of all cancer cases worldwide, with the highest rates in Australia and New Zealand, Europe, East Asia, and North America. It is the third most common cancer in men and the second most common cancer in women.
Certain lifestyle factors are now known to significantly increase the risk of colon cancer. The most common of these are poor diet, lack of exercise, smoking, and high alcohol intake. Genetics are also known to play a major role.
As with many diseases, early diagnosis can greatly increase the chances of survival. However, as symptoms are often non-existent until the later stages of the disease, many patients are unaware they are affected until it is too late. For this reason, awareness of the risk factors - along with regular screening - is crucial.
This article will cover everything you need to know about colon cancer, including the warning signs, diagnosis, and treatment. We’ll discuss preventative approaches and the importance of regular checkups, and how you can reduce the risk for yourself and loved ones.
The Basics: What Is Colon Cancer?
Colorectal cancer is a type of cancer that begins in the large intestine (colon) and/or the rectum. Cancers of the colon make up around two-thirds of colorectal cancers , while cancers of the rectosigmoid junction (between the sigmoid colon and the rectum) and the rectum itself make up one-third. Cancer of the small bowel (small intestine) is much more rare.
Colon cancer almost always originates from growths in the lining of the colon. These growths - called polyps - are most often benign, but abnormal cell growth can lead to the development of cancer. This can take around 5 to 15 years, and eventually invade the colonic wall. Around 75% of patients with polyps will have a parent who has had polyps, indicating a potential genetic link.
Early Symptoms and Warning Signs
Colon cancer develops very slowly. A polyp takes many years to become malignant. It is often not until stage 3 or 4 of the disease that noticeable symptoms occur. Even when the cancer has developed, it may be years before it is detected.
Possible signs of colorectal cancer include:
- Blood in the stool
- Bleeding and/or mucous in the anus
- Changes in bowel movements (for example, alternating between constipation and diarrhea)
- A feeling of fullness in the bowel or incomplete evacuation
- Persistent gas-like pain
- Pains or cramps in the abdomen or around the anus
- Unexplained weight loss
- Feeling tired and physically weak
Complicating a diagnosis of colorectal cancer, many ‘potential symptoms that patients may seek medical assistance with are also similar to that of other diseases, such as irritable bowel syndrome (IBS), gastritis, peptic ulcers, food intolerances, or inflammatory bowel disease. However, symptoms such as blood in the stool and unintentional weight loss should be taken seriously.
Genetics of Colon Cancer
While environmental factors play a part in all cancers, research shows that genetics are also involved. About 20% of colon cancer cases may have genetic factors, which makes it one of the most common inherited cancers.
First-generation relatives of colon cancer patients have three times the risk of developing cancer, while those who have two or more first- or second-degree relatives (or both) with colorectal cancer make up approximately 20% of all patients with the disease.
Genetic factors that may increase a person’s risk of colon cancer include:
- Strong family history of CRC and/or polyps
- Personal history of other cancers
- Family history of other cancers, such as endometrial cancer
- Early age at diagnosis
Approximately 5-10% of colon cancer is hereditary. The most common hereditary form is Lynch syndrome, also known as hereditary non-polyposis colorectal cancer syndrome (HNPCC). People with Lynch syndrome have up to 80% percent lifetime risk of colorectal cancer and up to 60% lifetime risk of endometrial cancer as well as increased risk for other primary cancers. Another hereditary colorectal cancer syndrome is Familial Adenomatous Polyposis (FAP), a genetic alteration that disrupts the function of the APC gene, increasing the risk of developing numerous colorectal polyps and thus the risk of colorectal cancer.
Types of Colon Cancer
The majority of all colon cancers are carcinoma (cancer that forms in epithelial tissue) and over 90% of those are adenocarcinomas. Less common types include adenosquamous, spindle, squamous and undifferentiated.
Other types of colon cancer include squamous cell tumors, carcinoid tumors, and sarcomas.
- Adenocarcinoma: A cancer of the cells lining the interior of the colon. Adenocarcinomas start in the mucous-producing gland cells in the lining of the bowel wall.
- Carcinoid tumors: A slow-growing cancer of the hormone-producing cells in the intestines. Also known as neuroendocrine tumors.
- Sarcomas: Cancers of connective tissues, such as bone or muscle. Most sarcomas in the bowel are called leiomyosarcomas, which means they begin in smooth muscle.
Stages of Colon Cancer
Stages of colon cancer are based on the size, location, and spread of the cancer within the body. The tumor–node–metastasis (TNM) system is used to refer to how far the tumor (T) has invaded the layers of the bowel wall; the number (N) of lymph nodes involved, and the extent of metastasis (M).
The earliest stage is 0, followed by stages 0-4.
Stage 1 cancer is limited to the bowel wall (T1, T2).
Stage 2 cancer affects the colon or rectum wall but not the lymph nodes.
Stage 3 means the cancer has spread to the first two inner layers of the colon or rectum wall or the lymph nodes.
In stage 4, the cancer has spread beyond the colon or rectum to other tissues and/or organs.
Risk Factors and Causes
All cancers - including colon cancer - are largely preventable. Despite evidence of genetic links, colon cancer has been strongly associated with certain lifestyle factors such as poor diet, low physical activity, regular alcohol intake, and cigarette smoking.
Healthy lifestyle choices, on the other hand, can significantly lower the risk. A large systematic review found that people with the healthiest lifestyles reduced their risk of colon cancer by around 48%. Another study suggested that healthy diet and better lifestyle habits may reduce the risk of colorectal cancer and prevent abnormal cell growth in up to 50% of cases.
Preventative strategies: Modifiable diet and lifestyle factors
Diet
The typical western Western diet is a major contributor to colon cancer risk due to its high intake of fat, red meat, and processed foods. Dietary factors shown to reduce the risk of developing cancer include:
- Increasing intake of dietary fiber.
Fiber can slow intestinal transit time and dilute carcinogenic compounds. Fiber also promotes the production of beneficial substances within the gut, such as short-chain fatty acids. - Eating plenty of fresh fruits, vegetables, and nuts.
These foods are rich in antioxidants such as vitamins C and E, which can protect against oxidative stress and slow cancer progression. Diets that were low in whole grains, milk, and calcium accounted for 81.61% of colorectal cancer deaths. - Supplementing with micronutrients.
Selenium and folate have been shown to have protective effects against colorectal cancer. People with high levels of selenium and folate are shown to have a substantially reduced risk of colon cancer. - Getting plenty of Vitamin D3
Vitamin D - which can be obtained from sun exposure - may lower the incidence of colorectal cancer by around 50%. Several studies show that increasing vitamin D3 levels reduces polyp recurrence and overall colon cancer incidence. Adequate levels of vitamin D3 are also associated with better survival rates of colon cancer patients. - Supporting gut health
Eating fermented foods and/or supplementing with probiotics. Probiotic bacteria supports gut microbiota and colonic epithelial cells, which can help protect against carcinogenesis.
Lifestyle factors
- Limiting alcohol
Moderate to heavy alcohol intake may increase the risk of colon or rectal cancer 1.2- to 1.5-fold. One study showed that a 10g increase in daily alcohol consumption increased the risk of colorectal cancer by around 7% overall. - Avoiding (or quitting) smoking.
Cigarette smoking is one of the most modifiable risk factors for CRC. Various studies have shown that smokers have a 15-60% higher risk of developing colon cancer. Quitting smoking for at least 20 years may greatly reduce the risk of developing colon cancer and/or facing adverse outcomes. - Exercising regularly
Physical activity and avoiding a sedentary lifestyle has enormous benefits for decreasing colorectal cancer incidence and mortality. One study found that physical activity of more than 6 METs (metabolic equivalents) hours per week reduced colon cancer risk by about 40%. People who were physically active before diagnosis are also found to have lower risk of cancer recurrence and death.
Role of Genetic Testing for Colon Cancer
Genetic testing involves checking DNA to determine any changes known to be associated with the development of cancer. Those with family history of cancer are strongly encouraged to undergo genetic testing to determine their level of risk, while those diagnosed are also advised to undergo genetic testing to determine the genetic risk for other family members.
Genetic testing can detect inherited colorectal cancer syndromes such as Lynch syndrome (also known as hereditary non-polyposis colorectal cancer, or HNPCC) or familial adenomatous polyposis (FAP). Preciseli has an easy at-home, comprehensive test for your genetic predisposition for colon cancer as well as over 18 other cancers. To sign up for the waitlist, click here.
Early Detection and Intervention
Significance of Early Screenings
Screening is one of the most important preventive measures against colon cancer. Over 75% of colon and rectal cancers occur in people with no obvious risk factors, which is why screening is crucial. It allows medical professionals to detect and remove cancer, polyps, or pre-cancerous growths, significantly increasing the chance of effective treatment.
Those aged 45 or over are encouraged to get regular colon screenings, especially if they have a family history of colorectal polyps or cancer.
Screening modalities range from stool samples, radiology-based tests, and endoscopic examinations (such as colonoscopies). Colonoscopy is the best method for finding and removing polyps.
Role of Healthcare Professionals in Early Detection
Primary care professionals are vital to the prevention and early detection of colorectal cancer. Most patients will seek medical advice for lower gastrointestinal symptoms before being diagnosed; it is the job of medical professionals to recognize and clinically assess potential cancer cases.
Understanding the Importance of Awareness
The greater the awareness of colon cancer, the more lives can be saved. A significant proportion of colon cancer-related deaths occur due to lack of knowledge about preventative strategies and screening options.
Colon Cancer Awareness is March, and the dark blue ribbon is worn to encourage those aged 45 and over to seek regular screening. This month also highlights the hereditary links of the disease, and the importance of familial impact, reminding those who have relatives with colorectal cancer that their risk is much higher.
The Colorectal Cancer Alliance was founded in 1999 by a group of colon cancer survivors and associates. As a patient advocacy organization, the CCA works to provide support for patients and families, caregivers, and survivors of colon cancer. It also helps to raise awareness of preventive measures; and inspire efforts to fund critical research.
The Takeaway
Awareness and understanding of colon cancer has improved vastly over the years. However, the high rate of diagnoses and deaths indicate that far too many people are still unaware of their risk, and why regular screening is so essential.
Understanding your family’s history of colon cancer - and any other genetic diseases - is the first step in being proactive about your own risk. Just one mutation in the numerous genes and proteins involved in cell division and DNA replication can lead to uncontrolled cancerous growth.
Regular screening is your best tool for prevention or early detection. The earlier that a cancerous or precancerous growth is detected and removed, the higher the chances of survival. Equally important is eating a healthy diet, exercising regularly, and limiting potentially harmful lifestyle factors such as alcohol consumption and smoking.
