Colorectal cancer (CRC) is a malignant growth of the lower intestine – this is the organ responsible for the removal of water and the formation of solid stool from food waste. The colon is approximately 90 cm. (3 ft.) long and ends at the rectum and anus. In cancer of the colon, cells from the inner lining divide in a rapid and uncontrolled fashion, resulting in a growth that invades local tissues and may spread to other parts of the body. Most cases of CRC develop from pre-existing polyps, which are collections of cells limited to the lining of the bowel, often assuming the shape of a mushroom suspended from the wall. As many as 30% of people have polyps, but fortunately, only a small number of these evolve into cancer. The evolution of cancer, including the formation of polyps and the transition to cancer, is a process that can take several years.
It’s important to note that polyps and early-stage cancer do not cause symptoms. During this pre-symptomatic period, these early cancers and precancerous growths can be identified and removed, resulting in the prevention and/or cure of colon cancer.
A risk factor is defined as something that increases your risk of develop colorectal cancer. The Canadian Cancer Society says most cancers results from many risk factors, but some colorectal cancers also develop in people who don’t have any. CRC risk factors include smoking, excessive alcohol consumption, a lack of physical inactivity, a personal history of colorectal polyps or colorectal cancer and being overweight, among others.
Age is an important risk factor for CRC, with 99% of cases occurring in people aged more than 40 and 85% in those aged more than 60.The incidence of colorectal cancer in younger adults has risen over recent years, but it is still an uncommon disease in young people. Medical experts have not discovered a cause for this increase as of now.
Race and ethnic background can increase your risk for CRC. African Americans and Jewish people of Eastern European descent (Ashkenazi Jews) statistically have the highest incidence of colon cancer. Those with Ashkenazi Jewish ancestry tend to have a mutation in the APC gene that increases the risk of colorectal cancer.
The strongest known risk factor for CRC is a family history of the disease. Individuals with a first-degree relative who has been diagnosed with CRC have two to four times the risk of someone without this family history. Some inherited diseases also increase the risk of developing colon cancer. One of the most common is called the Lynch syndrome.
Consuming approximately 45 grams of alcohol per day may increase the chances of developing colorectal cancer by 1.5 times versus a non-drinker.
Those who are obese, or overweight are more likely to develop colorectal cancer than those who are not. A high body mass index increases the risk for both men and women.
CRC is the most diagnosed cancer among men and the leading cause of cancer death in men younger than age 50 (Siegel et. al, 2020). In women, it ranks fourth (after breast, thyroid, and melanoma) and second (following breast) in terms of incidence and mortality.
Cigarette smoking is linked to an increased risk of CRC and death from colorectal cancer. Smoking tobacco is linked to an increased risk of forming colorectal adenomas, and even when removed, smokers are at an increased risk for adenomas to return.
For more risk factors visit the Canadian Cancer Society.
CRC may not present symptoms immediately as the cancer is very small. Symptoms often appear once a tumour grows into surrounding tissues and organs, and many of the CRC symptoms can also be caused by other issues such as hemorrhoids, irritable bowel syndrome, or inflammatory bowel disease. Symptoms of CRC include:
• Feeling that you need to have a bowel movement that is not relieved by having one
• Rectal bleeding with bright red blood
• Cramping or abdominal pain
• Weakness and fatigue
• Unexplained weight loss
• A change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts over a few days
• Swollen lymph nodes
• Stool (poop) that looks narrower than usual
If colon cancer spreads to other parts of your body, you may also encounter further symptoms:
• Blurry vision
• Bone fractures
• Difficulty breathing
If you are experiencing any of the above symptoms, consult your doctor for more information.
The following protective factors decrease the risk of CRC:
Through screening, colorectal cancer can be identified before symptoms are present– when the cancer is most curable. If you have no symptoms and are not at increased risk, you should still consider getting a screening examination. Screening can be done through a fecal immunochemical test, a safe and painless at-home cancer screening test. A flexible Sigmoidoscopy is another colorectal cancer screening test performed by a specialist (endoscopist). A third screening is called a colonoscopy, where a doctor can look at the entire colon, take biopsies, and remove polyps that can become cancerous over time. While there is dispute as to which screening strategy is most effective, there is a common consensus that persons who engage in CRC screening have a longer life expectancy than those who do not due to early diagnosis and treatment of CRC and removal of polyps before they turn malignant.
To learn more about CRC visit our Colon Cancer section.
1.Brenner, Hermann, and Chen Chen. “The Colorectal Cancer Epidemic: Challenges And Opportunities For Primary, Secondary And Tertiary Prevention”. British Journal Of Cancer, vol 119, no. 7, 2018, pp. 785-792. Springer Science And Business Media LLC, https://doi.org/10.1038/s41416-018-0264-x.
2. Ballinger, Anne B, and Clive Anggiansah. “Colorectal Cancer”. BMJ, vol 335, no. 7622, 2007, pp. 715-718. BMJ, https://doi.org/10.1136/bmj.39321.527384.be.
3. Lee, Sid. “Symptoms Of Colorectal Cancer”. Canadian Cancer Society, 2022, https://cancer.ca/en/cancer-information/cancer-types/colorectal/signs-and-symptoms.
4. Lowery, Jan T. et al. “Understanding The Contribution Of Family History To Colorectal Cancer Risk And Its Clinical Implications: A State-Of-The-Science Review”. Cancer, vol 122, no. 17, 2016, pp. 2633-2645. Wiley, https://doi.org/10.1002/cncr.30080.
6. “Screening For Colorectal Cancer”. Cancer Care Ontario, 2022, https://www.cancercareontario.ca/en/types-of-cancer/colorectal/screening.
5. “Colon Cancer Information | Mount Sinai – New York”. Mount Sinai Health System, 2022, https://www.mountsinai.org/health-library/diseases-conditions/colon-cancer.