Colorectal cancer screening: colonoscopy, tests and recommended age
Colorectal cancer (including rectal cancer) is one of the few cancers that can be prevented through screening. Precancerous polyps can be identified and removed before becoming cancerous, and cancers detected at early stages have cure rates over 90%. Despite this, many people avoid or postpone screening.
Why screening matters
The numbers count
- Colorectal cancer is the third most common cancer worldwide
- Detected at stage I, the 5-year survival rate is over 90%
- Detected at stage IV, the rate drops to under 15%
- Screening reduces colorectal cancer mortality by 40-60%
How screening prevents cancer
Most colorectal cancers develop from adenomatous polyps — small growths on the intestinal mucosa. The transformation of a polyp into cancer usually takes 10-15 years. Screening detects and removes polyps before they become malignant.
Types of screening tests
Colonoscopy — the gold standard
What it is: Examination of the entire colon and rectum with a flexible endoscope (thin tube with a camera at the tip), under sedation.
Advantages:
- Examines the entire colon (the most complete method)
- Allows biopsy and polyp removal in the same procedure
- If normal, repeated only after 10 years
Disadvantages:
- Requires bowel preparation (a cleansing solution with an unpleasant taste)
- Done under sedation — you need a companion
- Rare risks: perforation (1 in 1000-3000), bleeding (1 in 100-200 with polypectomy)
- A day off work
How it is done:
- Preparation (the day before): liquid diet + bowel cleansing solution
- Procedure (30-45 minutes): IV sedation, scope insertion, examination of the mucosa
- After (1-2 hours): recovery from sedation, you can eat normally
- Result: immediate (if polyps are found, they are sent for histology — result in 1-2 weeks)
Flexible sigmoidoscopy
What it is: Examination of only the last 60 cm (24 in) of the colon (sigmoid and rectum), without sedation.
Advantages:
- Simpler preparation (just an enema)
- No sedation required
- Fast (15-20 minutes)
Disadvantages:
- Examines only the left half of the colon — may miss right-sided lesions
- If polyps are found, full colonoscopy is also needed
Fecal Immunochemical Test (FIT)
What it is: A test that detects occult blood (invisible to the naked eye) in stool, using antibodies specific to human hemoglobin.
Advantages:
- Simple — done at home, without preparation
- Painless — only collecting a stool sample
- Cheap and widely available
- No diet or medication changes needed
Disadvantages:
- Only detects bleeding lesions — may miss polyps and cancers that don’t bleed
- Repeated annually — a single test is not enough
- If positive, colonoscopy is needed for confirmation
- False-positive results possible (hemorrhoids, anal fissures)
Frequency: annually
Stool DNA test (Cologuard)
What it is: A test that detects both occult blood and DNA mutations specific to cancer in the stool sample.
Advantages:
- Done at home
- Higher sensitivity than simple FIT for cancer (92% vs 74%)
- Also detects advanced polyps
Disadvantages:
- More expensive than FIT
- Limited availability
- Higher rate of false-positive results
- If positive, requires colonoscopy
Frequency: every 3 years
CT Colonography (virtual colonoscopy)
What it is: A CT scan of the colon after air insufflation, creating 3D images of the intestinal mucosa.
Advantages:
- Non-invasive (no scope inserted)
- Fast (15 minutes)
- May also detect extra-colonic lesions
Disadvantages:
- Requires the same bowel preparation as colonoscopy
- Does not allow biopsy or polyp removal
- Radiation exposure
- Polyps under 6 mm can be missed
Frequency: every 5 years
Recommended age for screening
General population (average risk)
| Organization | Starting age | Recommended method |
|---|---|---|
| American Cancer Society | 45 | Colonoscopy or annual FIT |
| US Preventive Services Task Force | 45 | Any validated method |
| European guidelines | 50 (some countries 45) | Annual FIT + colonoscopy if positive |
Higher risk — earlier screening
Family history of colorectal cancer:
- First-degree relative (parent, sibling, child) diagnosed under 60: colonoscopy starting at 40 or 10 years before the relative’s diagnosis age
- First-degree relative diagnosed over 60: colonoscopy from 40
Genetic syndromes:
- Lynch syndrome: colonoscopy from 20-25, every 1-2 years
- Familial adenomatous polyposis (FAP): sigmoidoscopy from 10-12, annually
- Other syndromes: as recommended by the geneticist
Inflammatory bowel disease:
- Ulcerative colitis or Crohn’s disease with colon involvement: colonoscopy starting 8 years after onset, then every 1-3 years
Abdominal or pelvic radiation:
- Colonoscopy from age 30 or 5 years after radiotherapy
What happens if polyps are found
Types of polyps
- Hyperplastic polyps — usually benign, no malignant potential
- Tubular adenomas — precancerous potential, but low risk if small
- Villous adenomas — higher risk of malignant transformation
- Advanced adenomas — over 10 mm, with villous component or high-grade dysplasia
- Sessile serrated polyps — precancerous potential, harder to detect
After polypectomy — next colonoscopy
| Result | Next colonoscopy |
|---|---|
| No polyps | 10 years |
| 1-2 small tubular adenomas (under 10 mm) | 7-10 years |
| 3-4 small adenomas | 3-5 years |
| 5+ adenomas or advanced adenomas | 3 years |
| Large sessile serrated polyp | 3 years |
| Polyp with cancer (pT1) | 1 year (after full assessment) |
Barriers to screening
Why people avoid colonoscopy
- Fear of the procedure — “it’s painful” (in fact, under sedation you feel nothing)
- Embarrassment — shame about the area examined
- The preparation — the cleansing solution is unpleasant (but bearable)
- No symptoms — “I feel fine, why go” (early cancer DOES NOT cause symptoms)
- Lack of information — many don’t know that screening exists or is recommended
- Cost — varies by country and insurance
The reality
- Colonoscopy under sedation is painless — most patients say the prep was worse than the procedure itself
- The procedure takes 30-45 minutes
- You go home the same day
- The discomfort of the prep lasts one evening — but protects you for 10 years
Frequently asked questions
Is colonoscopy painful?
Under sedation, you feel nothing. You wake up after 30-45 minutes without realizing time has passed. Some patients have mild bloating after the procedure, which goes away in a few hours.
How long does the prep take?
Preparation starts the day before: liquid diet during the day and the cleansing solution in the evening (and sometimes early morning). The effect lasts a few hours — stay close to a toilet.
Can I have a colonoscopy without sedation?
Yes, but not recommended. Discomfort can be significant and may compromise the quality of the examination.
How often should it be repeated?
- Normal colonoscopy: in 10 years
- Negative FIT: annually
- If polyps were found: in 3-5 years (depending on type and number)
This article is for informational purposes only and does not replace medical consultation. Discuss with your family doctor about the optimal time for colorectal screening.