Colonoscopy/Colorectal Cancer Screening

The frequency of colorectal cancer is dropping in those countries that advocate a widespread use of colonoscopy for cancer screening.


Colorectal cancer normally develops when a benign growth (called an adenoma or polyp) in the intestinal mucosa becomes malignant (carcinoma). This process, which is called the adenoma-carcinoma sequence, can take up to 10 years and often goes unnoticed during most of this time. However, the early stages of cancer that typically form in the large intestine (colon) or rectum can be detected by using appropriate examination techniques such as a colonoscopy.

Because colorectal cancer develops from its pre-cancerous forms quite slowly, effective early detection is possible. If early cancer screening does find indications of suspicious growths in the intestines, a colonoscopy can be used to diagnose and to remove them. This process usually halts the risk of cancer before it can progress, meaning that early colorectal cancer screening is significant for cancer prevention.

As a result, the frequency of colorectal cancer has been decreasing for years in countries with screening colonoscopy programs in place.

Colorectal cancer is a serious health issue: In western countries, colorectal cancer is the second-most common form of cancer in women and the third-most common in men.

The risk of developing colorectal cancer increases with age, with more than half of all cases affecting people ages 70 and above. In contrast, only about 10% of people with colorectal cancer are below the age of 55 years old.

Colorectal cancer develops when cells in the intestinal mucosa begin to divide uncontrollably due to genetic changes (mutations). This leads to the formation of a tumor that can grow and spread into blood vessels or other surrounding tissues. During this process, malignant cells from the tumor can also break free and form new tumors in other parts of the body (called metastases).

It is usually not possible to determine why colorectal cancer develops in some people and not others. The risk of developing colorectal cancer is higher for people with first-degree relatives who have been diagnosed with colorectal cancer. Some other conditions like ulcerative colitis have also been linked to a higher risk of colorectal cancer.

The main warning sign of colorectal cancer is bloody stools. Additionally, altered bowel movement habits can also be an indication of the disease, for example alternating between constipation and diarrhea, or feeling the urge to defecate more often than usual but without actually passing more stools. Stools that are as thin as a pencil may be also a warning sign.

Other symptoms of colorectal cancer include recurring abdominal cramps, loud abdominal sounds, persistent flatulence, stools with a pungent odor, and areas of the abdomen that feel firm to the touch. A diagnosis of cancer should also always be kept in mind when general symptoms like decreased energy, unusual fatigue, or unintended weight loss occur.

Diagnosis/early detection

Different examinations are performed for the early detection and prevention of colorectal cancer. These include manually probing the rectum (digital rectal examination) and a test for invisible (occult) blood in stool (fecal occult blood test).

Colorectal cancer can also be prevented through individual lifestyle changes. These work by helping people avoid risk factors that lead to colorectal cancer, primarily smoking and obesity. A lack of movement, low-fiber diet, excessive alcohol consumption, or eating raw meat can all increase the risk of colorectal cancer.

An immunological test for fecal occult blood may be performed as part of the early colorectal cancer detection process. This stool test consists of a tube with an integrated stick that is used to collect a stool sample which is then turned in at the doctor’s office or sent by mail to a special laboratory for analysis. If blood is detected in the stool sample, the results should be further examined by colonoscopy.

However, blood in stool does not automatically mean colorectal cancer. It might also be caused by other conditions like hemorrhoids, inflammatory bowel disease, or diverticular disease (diverticulitis). A colonoscopy can also detect the presence of an inflammatory bowel disease like Crohn’s disease or diverticulitis.


Colonoscopies are crucial to confirm a diagnosis of colorectal cancer in the rectum or colon. If the examination detects adenomas, which are a precursor of cancer, they can be removed during the same examination, which prevents them from later developing into a malignant tumor. If the results of the colonoscopy are normal, it should be repeated every 10 years or shorter – depending on the situation of the individual patient.

For people with a high risk of cancer, for example with known cases of colorectal cancer among relatives, a colonoscopy may be advisable earlier than in the rest of the population. In this case, the first colonoscopy should generally be performed at least 10 years before the age at which the relative was diagnosed with cancer.

A colonoscopy is also recommended any time a person experiences symptoms consistent with colorectal cancer, regardless of their age.

In order for a colonoscopy to be performed properly, it is always necessary to purge the digestive tract beforehand. A bowel cleanse is carried out to completely empty the digestive tract of any stool or other undigested food, which allows the intestinal mucosa to be easily visible and properly evaluated during the examination.

Therefore, no foods that are difficult to digest should be eaten for two days before the colonoscopy. Solid food may not be eaten for about 20 hours before the examination, and patients must drink a special bowel cleansing agent (such as a polyethylene glycol solution (PEG)) that thoroughly empties the small and large intestines.

A colonoscopy is performed using a flexible tube about the same thickness as a finger that is equipped with a light source and a camera at its front end (endoscope, colonoscope) that illuminates and records the inside of the entire colon. The colonoscope is inserted into the rectum and moved forward through the different segments of the large intestines. As the instrument is slowly withdrawn, the doctor is able to view the intestinal mucosa on a screen at several different zoom factors. If the doctor observes suspicious-looking tissue, he or she can remove a sample of this tissue using small forceps pushed through the tube in order to examine it later under the microscope. Some stages of cancer, like polyps, can also be completely removed during the colonoscopy itself using small forceps or a loop.

A colonoscopy is usually performed after complete emptying of the digestive tract and under light sedation in a gastroenterology practice or as an outpatient procedure at a hospital.

In addition to conventional colonoscopy, a virtual colonoscopy can also be performed by computed tomography (CT colonography) or magnetic resonance imaging (MRI colonography). These are performed by taking many layered images of the interior of the body and using them to recreate a three-dimensional image of the insides of the intestines with the help of special software programs. These techniques do not require the insertion of a colonoscope into the colon. However, in contrast to conventional colonoscopy, these methods also do not allow for tissue collection, and any suspicious areas cannot be removed directly during the examination.