Colon Cancer Risk Factors, Screening and Diagnosis

Risk Factors and Screening

The colon is the lower part of our digestive system, also known as the large intestine. Doctors distinguish the colon from the rectum due to their differences in function. The rectum is the very last 7-8 inches of the colon where stool is stored immediately prior to elimination. The colon performs important functions of reabsorption of salt and water from our digested food so as to create solid stool from the primarily liquid digestive matter which reaches the colon from the small intestine. Colorectal cancer is used as a general term for malignancies involving either part, but as will be discussed later, the treatments and outcomes are slightly different.

Colorectal cancer can affect anyone of any age, but clearly the risk increases with age. Only 10% of cases occur in those less than 40 years of age, but as we approach 50 and beyond, our risk doubles each decade of life. Most cancers (60%) are sporadic which means there is no family history or genetic syndrome involved. There are approximately 150,000 new cases of colorectal cancer in the US annually, and 6% of the population will develop this type of malignancy during their lifetime. It is the second leading cause of death from cancer for both men and women and affects the sexes equally.

Of the colorectal cancers which are not sporadic, there are familial and hereditary. Familial means there are others in the family who had previously been affected, but there is no known genetic mutation that has been passed along. Hereditary means there is a specific gene that is known and shown to be mutated, and comprise 10% of all colorectal cancers. Such syndromes include HNPCC (Hereditary Non-polyposis Colon Cancer aka Lynch Syndrome), FAP (Familial Adenomatous Polyposis) and MAP (MYH associated polyposis).


Cancers of the colon and rectum start as polyps. There are two kinds of polyps called adenomatous and hyperplastic polyps, but most are adenomas and for practical purposes, the terms polyp and adenoma are often used synonymously. The adenomas are pre-cursors to colon cancer but the hyperplastic ones are not. These are benign growths that start on the internal lining of the lower digestive system. What causes their initial growth is difficult to determine, but likely an interaction of one’s environment and diet as well as genetic mutations that occur in our body frequently. Regardless these initial polyps are benign and cause no symptoms, but left unchecked can evolve into a malignancy within typically 7-10 years.

View of a polyp taken during a colonoscopy. View of a colon cancer taken during colonoscopy.


Colon cancer is one of the few cancers that can be prevented. The prevention is called colonoscopy and polypectomy. Epidemiologic studies have shown that for someone of average risk, the risk of harboring polyps in one’s colon is 10% at age 50 and then doubles each decade of life. Since, as stated above, the condition creates no symptoms, it is imperative to undergo colonoscopy to identify if you have polyps or not. If so, the polyps can be removed easily with little risk during the colonoscopy, thus greatly reducing your odds of developing colon cancer. There are other methods of screening for colorectal cancer such as fecal occult blood testing combined with flexible sigmoidoscopy or barium enema, or virtual colonoscopy. These methods are not nearly as accurate as colonoscopy and fail to allow for the important intervention of polypectomy should something be found. Therefore, these methods are used primarily as alternatives for patients who are deemed high risk for colonoscopy.



If you have a first degree relative (parent or a sibling) with colorectal cancer your risk is two times higher of developing polyps and cancer. Therefore, it is recommended that such individuals undergo screening colonoscopy at age 40 or 10 years earlier than the time of diagnosis of the affected family member, whichever comes first. African Americans have higher rates of colorectal cancer and should start screening at age 45.

Certainly patients who present with unexplained rectal bleeding should be considered for colonoscopy regardless of age. Although rectal bleeding is often from hemorrhoids, this assumption is dangerous to make on your own. Other symptoms of colorectal cancer to be aware of include:

  • Change in bowel habits, especially more frequent and looser stools.
  • Bloating or cramping with defecation.
  • The feeling of incomplete evacuation after defecation
  • General abdominal pain
  • Unintentional weight loss, especially with loss of energy, endurance, or appetite.

In most circumstances it may be safer to undergo colonoscopy to exclude other more serious conditions such as cancer prior to concluding that the sole cause of one’s bleeding is hemorrhoids. This should be discussed with your physician.


Colorectal Cancer Screening Guidelines

American Society of Colon and Rectal Surgeons – 2006

“There is no relationship between hemorrhoids and cancer. However, the symptoms of hemorrhoids, particularly bleeding, are similar to those of colorectal cancer and other diseases of the digestive system. Therefore, it is important that all symptoms are investigated by a physician specially trained in treating diseases of the colon and rectum and that everyone 50-years or older undergo screening tests for colorectal cancer.” Rectal bleeding should not then be assumed due to hemorrhoids until colorectal cancer and other digestive diseases have been ruled out as a possible cause.

Medicare Guide to Preventative Services – April 2007
Colorectal Cancer Screening Tests
• Fecal Occult Blood (FOBT)

• Flexible Sigmoidoscopy
• Colonoscopy
• Barium Enema

Unless the words “High Risk” are specified, all of the following guidelines are for patients who are at a normal risk for developing colorectal cancer:

High Risk Factors

• A sibling, parent, or child had an adenomatous polyp or colon cancer
• Family history of adenomatous polyposis or hereditary colorectal cancer
• A personal history of adenomatous polyps, colorectal cancer, or Inflammatory Bowel Disease (IBD)

A patient is at “high risk” if he has any of these above risk factors.

After age 50, all annual time periods listed below are given a 30 day grace period; whereby the physician may commence Colorectal Cancer Screening up to 30 days earlier than specified:

Medicare Covered Fecal Occult Blood (FOBT)
• Annually if age 50

Medicare Covered Flexible Sigmoidoscopy
• Beginning age 50, then once every 4 years

Medicare Covered Colonoscopy
• Once every 2 years for a patient with high risk factors (without regard to age)
• Beginning age 50, then once every 10 years
• Must be at least 4 years after a Flexible Sigmoidoscopy.

Medicare Covered Barium Enema

• As an alternative to Colonoscopy of Flexible Sigmoidoscopy
• Once every 2 years for a patient with high risk factors (without regard to age)
• Beginning age 50, then once every 4 years
• Preferably a double contrast Barium Enema


American College of Gastroenterology (ACG) Guidelines – March 2009:

1) The starting age is lowered to 45 years for African Americans. Perhaps also at age 45 years, for patients who are obese or who have an "extreme smoking history."

2) It is reasonable to consider screening at an age earlier than 50 years (i.e. 45 years) in patients with characteristics known to promote colorectal cancer, including a history of smoking and obesity (defined as a BMI >30). However, there is no formal recommendation for earlier screening in these subgroups of patients at this time.

3) If the colorectal cancer or advanced adenoma in the first-degree family member is diagnosed at younger than 60 years, or if there are 2 first-degree relatives with colorectal cancer or advanced adenoma, screening colonoscopy should begin at age 40 years, or 10 years younger than the age at diagnosis of the youngest affected relative. Colonoscopy should be repeated at 5-year intervals for these patients.

4) Patients with familial adenomatous polyposis should undergo annual flexible sigmoidoscopy or colonoscopy until colectomy is performed.

5) Another preferred screening test is annual Fecal Immunochemical Test (FIT). A previous study found that FIT was superior to older guaiac-based fecal occult blood tests to detect both advanced adenomas and colorectal cancer in adults being screened for colorectal cancer; and because fecal DNA testing is too expensive.

6) Alternative and less-preferred screening tests for colorectal cancer include flexible sigmoidoscopy every 5 years, or computed tomographic colonography every 5 years. Double-contrast barium enema testing is no longer part of the screening recommendations for colorectal cancer. Its use has declined dramatically, and computed tomographic colonography is more effective in diagnosing polyps.

7) In the current recommendations from the ACG, colonoscopy is the test of choice to screen for colorectal cancer. Annual screening with FIT is the first alternative to colonoscopy screening, followed by flexible sigmoidoscopy and computed tomographic colonography. Double-contrast barium enema to screen for colorectal cancer is no longer recommended.