Colon (aka colorectal) cancer starts in the large intestine, which is the looooong windy tube that helps carry digested food to the rectum and out of the body. Cancer that develops in this part of the body typically starts as a polyp, or a growth, in the colon’s inner lining. Over time, some (but not all) polyps can become cancerous…but here’s the good news: it usually takes about ten years for this to happen. And there are several effective screening tools to spot and remove the polyps first.
4 colon cancer screening tests
- Stool tests
Some test for the presence of blood using chemicals (what’s called a guaiac-based fecal occult blood test) while others use antibodies (fecal immunochemical test). A third option is an mt-sDNA test, which aims to find cancer DNA in the sample. Some require just a small stool sample while others require the entire bowel movement.
- Flexible sigmoidoscopy
Here, your doctor will insert a short lighted tube into the rectum to check for polyps or cancer in the rectum and lower third section of the colon.
This procedure is similar to a flexible sigmoidoscopy except the doctor will check inside the rectum and the entire colon, not just the lower section. During a colonoscopy, the doctor can also find and remove most polyps as well as certain cancers.
- CT colonography
Also known as a virtual colonoscopy, computed tomography (CT) colonography is when doctors use X-rays to image and analyze the colon.
The decision around which test is right for you should be made with your primary care provider or gastroenterologist based on personal health history and risk factors…more on that below.
Types of polyps
Precancerous polyps come in two different shapes: some are flat (or “sessile”) and others have a stalk (known as “pedunculated” polyps). Shape aside, there are five types that your doctor can find in a colonoscopy or sigmoidoscopy, not all of which will turn into cancer.
- Adenomatous (tubular adenoma): the most common type (at about 70%), although less than 10% become cancerous
- Hyperplastic: type of serrated polyp that’s common but poses a very low cancer risk
- Sessile serrated: flat, difficult-to-detect polyps usually located in the upper colon area
- Inflammatory: common among those with Inflammatory Bowel Disease (IBD) and pose a very low cancer risk (because they’re not true polyps but rather a reaction to chronic inflammation)
- Villous adenoma (tubulovillous adenoma): sessile (flat), difficult to remove, and a high risk for turning cancerous
When should I start colonoscopy screenings?
According to the U.S. Preventive Services Task Force screening guidelines, adults 45-75 should be screened for colon cancer.
How often should women get a colonoscopy?
It’s recommended that adults without an increased risk of colorectal cancer get a colonoscopy every 10 years. If you’re opting for a flexible sigmoidoscopy, however, the recommendation is every five years for those at average risk.
More regular screenings and follow-ups are required if polyps are found:
- Every three years if 3-4 polyps <1 cm in size are found or one polyp >1cm is found
- Every year is at least five small or three larger polyps are found
If you’re at higher risk for colon cancer (more on that below), the age in which you start screenings, as well as your screening frequency, may look different. As always, it’s best to check with your doctor to understand your individual risk.
Important! Even if you’re not due for a colonoscopy, you should see your doctor if you’re experiencing any of the following symptoms:
- A change in bowel habits (including diarrhea, constipation, and/or a feeling that the bowel does not empty all the way)
- Blood in or on the stool
- Persistent abdominal pain, aches, or cramps
- Unexplained weight loss
Who is at a higher risk of developing colon cancer?
There are certain factors that increase one’s risk of colon cancer, many of which are within our control. Here are the main ones, according to The American Cancer Society:
Being overweight or obese
Lack of physical activity
It’s estimated that exercise can prevent approximately 15% of all colon cancers.
Diets high in red meats and processed meats are thought to be associated with an increased risk of colon cancer, especially if meats are cooked at high temperatures. Low vitamin D levels are also thought to increase our risk.
Type 2 diabetes
Those with type 2 (non-insulin dependent) diabetes have an estimated 27% higher risk of developing colon cancer — even after taking factors like obesity and lack of physical inactivity into account (which are common risk factors for both type 2 diabetes and colon cancer).
Long-term cigarette smoking is associated with a 20-60% higher risk of colon cancer.
Although the relationship between alcohol use and rectal cancer/colon cancer is stronger for men than women, studies have identified a link among both sexes.
Our risk for colon cancer increases after age 50 — although it should be noted that the rate of colon cancer diagnoses among younger individuals is increasing. In fact, in early 2023, the American Cancer Society reported that 20% of all diagnoses in 2019 were patients under 55 (double the rate in 1995).
Personal or family history of colorectal cancer
It’s estimated that as many 16-20% of people who develop colon cancer have a first-degree family member who has had it.
Other inherited syndromes that may increase one’s risk include Lynch Syndrome (aka hereditary nonpolyposis colorectal cancer syndrome) and familial adenomatous polyposis (FAP).
Personal history of Inflammatory Bowel Disease (IBD)
IBD is characterized by inflammation in the digestive tract lining — the most common types are Ulcerative Colitis or Crohn’s Disease. If untreated, IBD can develop into dysplasia. This is when abnormalities are found in the colon cells which, while not immediately cancerous, often become cancerous over time.
Important: Inflammatory Bowel Disease (IBD) is different from Irritable Bowel Syndrome (IBS), which does not increase the risk of colorectal cancer.
Racial & ethnic background
Black Americans have the highest incidence of colon cancer in the United States at 41.9 per 100,000 (along with the highest rates of mortality). Native Americans follow closely at 39.3 per 100,000. For comparison, White Americans have an incidence rate of 37 per 100,000.
The bottom line
Preventative health screenings are no fun — no one WANTS to go for a pap smear or a colorectal cancer screening. But we have to think of this as a short-term inconvenience in service of long-term health and wellness. We want to be healthy and living our BEST lives for as long as possible, and that work happens now. Future you will thank you.