Explained
Colorectal cancer screening: who needs it and when
Colorectal cancer is one of the few cancers screening can prevent outright — not merely find earlier.
Why screening prevents rather than just detects
Most cancer screening finds disease earlier. Colorectal screening can do something better: it can stop the cancer from ever forming.
The great majority of colorectal cancers begin as a polyp — a small growth on the inner lining of the bowel. Most polyps never become cancer. But the ones that do usually take years to make that change.
That slow timeline creates a long window. If a colonoscopy finds a polyp during that window, it can usually be removed during the very same procedure. The potential cancer is gone before it existed.
Very few cancers offer that. It is the single most important thing to understand about this disease.
Who should consider it
Bangladesh does not have a national colorectal screening programme, so in practice this is a conversation between you and your doctor rather than an invitation letter that arrives in the post. That makes knowing your own risk more important.
- Age. Risk rises with age, and international guidelines generally begin screening average-risk adults somewhere in the 45–50 range.
- Family history. A parent, sibling or child with colorectal cancer or advanced polyps means starting earlier and repeating more often.
- Inherited syndromes. Conditions such as familial adenomatous polyposis or Lynch syndrome require a specific surveillance plan, often from a young age.
- Inflammatory bowel disease. Long-standing ulcerative colitis or Crohn's colitis increases risk and calls for planned surveillance.
- Previous polyps. If polyps have been found before, the interval to your next colonoscopy is set by what was found.
Because there is no automatic system here, the practical advice is simple: if any of the above applies to you, raise it at your next consultation rather than waiting to be asked.
What a colonoscopy involves
The examination itself is straightforward. A flexible tube with a camera is passed through the bowel so the lining can be inspected directly. It is usually done with sedation, and most patients remember very little of it.
The part patients find harder is the preparation the day before — a bowel-cleansing solution that empties the colon so the lining can be seen clearly. It is inconvenient rather than painful, and it matters: a poorly prepared bowel can hide exactly what the test is looking for.
- Follow the diet instructions in the days beforehand precisely
- Take the preparation exactly as timed, however unappealing it is
- Tell the team about blood thinners, diabetes medication and any heart or lung condition well in advance
- Arrange for someone to accompany you home if sedation is used
The great advantage over stool-based tests is that a colonoscopy is not only diagnostic. If something is found, a biopsy can be taken and a polyp can be removed then and there.
Do not wait for symptoms
This is the part that costs people most.
Early colorectal cancer very often produces no symptoms at all. By the time symptoms are obvious — persistent bleeding, a marked change in bowel habit, weight loss, anaemia — the disease has usually been present for some time.
Screening exists precisely because waiting for symptoms means waiting too long.
- Blood in the stool, or bleeding from the back passage
- A change in bowel habit lasting more than a few weeks
- Unexplained weight loss
- Unexplained iron-deficiency anaemia
- Persistent abdominal pain, or a feeling of incomplete emptying
Do not assume piles. Piles are common, they can coexist with something else, and assuming is how years get lost.
Reducing risk in daily life
Screening is the main tool, but lifestyle contributes:
- More fibre — vegetables, fruit, whole grains, pulses
- Less processed meat and less red meat
- Regular physical activity
- Maintaining a healthy weight
- Stopping smoking
- Limiting alcohol
None of this replaces screening. A healthy diet does not remove a polyp — a colonoscopy does.
Common questions
At what age should screening start?
For someone at average risk, international guidelines generally suggest starting somewhere in the 45–50 range. With a family history or bowel disease it should begin earlier. Your own starting point is best decided with your doctor.
Is colonoscopy painful?
It is usually done under sedation and most patients remember little of it. The bowel preparation the day before is the part people find most inconvenient.
How often does it need repeating?
That depends on what the first examination shows. A normal result in an average-risk person means a long interval; finding polyps means a shorter one. Your endoscopist will specify it.
Are stool tests an alternative?
Stool-based tests can flag people who need further investigation, and they are useful where colonoscopy is not readily accessible. But a positive result still means a colonoscopy, and a stool test cannot remove a polyp.
If nobody in my family has had it, am I safe?
Most people diagnosed with colorectal cancer have no family history at all. Family history raises risk; its absence does not remove it.
I have piles — could that explain my bleeding?
It might, and often does. But piles and a colorectal tumour can be present at the same time, and neither the colour of the blood nor the presence of piles rules the other out. It needs to be looked at properly once.
This article is general patient information and does not replace a consultation. If your symptoms are severe or getting worse, please see a doctor rather than relying on it.
Have a question about this?
Bring your reports to a consultation — often one visit settles it.