What Is Colorectal Cancer?

Here's the puzzle that makes this cancer different from most others: it can grow quietly for a long time, cause no symptoms at all, and still be found — and stopped — by a test you were offered when you felt perfectly well. Colorectal cancer is cancer that starts in the colon or the rectum, the last sections of the large intestine. It is also called colon cancer, rectal cancer, or bowel cancer, depending on exactly where it begins.

The short video at the top of this page, "Colon and Rectal Cancer" (about two minutes), puts the definition plainly: this is the development of cancer in the colon or rectum, arising from the abnormal growth of cells. The questions below take that definition and walk through what patients actually ask next — where it comes from, how anyone would know, and what happens after a diagnosis. For broader background, our cancer condition hub gathers related guides and videos in one place.

Where in the bowel does it start, and why there?

Your large intestine is a long tube whose lining renews itself constantly. That constant renewal is useful — the lining takes a daily beating from everything passing through — but it also means lots of cell division, and over years some clusters of cells can start growing in a less orderly way.

Most colorectal cancers begin as a polyp: a small growth projecting from the inner lining. Not every polyp is dangerous, and most never become cancer. But one family of polyps, adenomas, can change slowly over years and is the usual starting point for this cancer. That slow timeline is the whole reason screening works so well here — there is a long window in which a growth can be found and removed before it turns into anything more serious. If that idea is new to you, our guide to what colon polyps are explains how they are found and removed, and what the laboratory result means.

If it can be silent, how is it ever found?

Two roads lead to a diagnosis. The first is screening: testing people who have no symptoms. Screening can mean a stool-based test that looks for hidden blood or other markers, or a direct look inside the bowel with a camera test such as colonoscopy. A camera test has a double benefit — the clinician can see the lining and remove polyps during the same procedure. Our guide to what a colonoscopy is and how it is done walks through the preparation, the procedure itself, and recovery, and the colonoscopy hub collects the related videos.

The second road is symptoms that prompt investigation. Changes worth discussing promptly with your own clinician include a lasting change in bowel habit, blood in or on the stool, ongoing abdominal discomfort, unexplained weight loss, or persistent tiredness that could reflect anaemia. None of those signs proves cancer — each has many more common causes — but each deserves a proper assessment rather than months of waiting to see. If you'd like a second, longer look at the condition itself, "Colon cancer" (just under three minutes) collects further information on cancer of the colon and rectum.

What happens if a test finds something suspicious?

A suspicious area is not a diagnosis on its own. During a colonoscopy, the clinician can take small tissue samples — biopsies — or remove a polyp whole, and that tissue goes to a laboratory. It is the pathologist's examination under the microscope that confirms whether cancer is present and what type it is.

If cancer is confirmed, the next phase is staging: finding out how far it extends. That usually involves scans of the abdomen and chest, blood tests, and a detailed review of the biopsy findings. Staging sounds like paperwork, but it is what shapes treatment — a small cancer confined to a polyp is handled very differently from one that has reached nearby lymph nodes or beyond. Your team will explain the stage in plain terms and what it means for the plan they are recommending.

What do the main treatments look like?

Surgery is the central treatment for most colorectal cancers that have not spread widely: removing the section of bowel containing the cancer, together with nearby lymph nodes, so the laboratory can check them. Depending on where the cancer sits and how the bowel is rejoined, a stoma — an opening of the bowel onto the abdomen — is sometimes needed, temporarily or permanently. Your surgeon will discuss whether that is likely in your case before the operation, not after it.

Other treatments are added according to the stage and the exact situation. Chemotherapy may be offered after surgery to lower the chance of the cancer returning, or before surgery in some rectal cancers. Radiotherapy has a particular role in rectal cancer, where shrinking the tumour first can make surgery more effective. For cancer that has spread, treatment focuses on medicines that can control the disease, given by oncology teams who tailor the choice to the tumour's characteristics and to you. There is no single recipe here — which is precisely why decisions are made by a multidisciplinary team rather than one clinician alone.

Can anything lower the risk?

No habit guarantees protection, and people who do everything "right" can still develop this cancer. That said, screening is the strongest tool most of us have, because it does not just find cancer early — by removing adenomas, it can prevent some cancers from starting at all. Taking up a screening invitation when it arrives, and not shelving it, matters more than any single lifestyle tweak.

Beyond screening, general measures that support bowel health — staying active, keeping a healthy weight, eating a diet rich in fibre and lower in processed meat, not smoking, and moderating alcohol — are associated with lower risk. Family history also counts: if close relatives have had colorectal cancer or advanced polyps, tell your clinician, because it can change when screening should start and how often it should happen. Those personal decisions belong in a conversation with your own doctor, who knows your history.

What does follow-up look like after treatment?

Treatment ending is not the story ending. Follow-up usually combines clinic visits, blood tests, scans at intervals your team sets, and surveillance colonoscopies to watch the remaining bowel — people who have had one colorectal cancer or advanced polyps have a higher chance of developing new polyps. The schedule is individual, and it often stretches over years, gradually spacing out if all stays well.

Living after treatment also includes the practical and emotional side: adjusting to a changed bowel habit, managing fatigue, and coping with the anxiety that scans can bring. Support from your clinical team, stoma nurses if relevant, and reputable patient organisations can make that phase easier — ask what is available locally rather than assuming you have to manage it alone.

References & further reading

• MedlinePlus — Colorectal Cancer: https://medlineplus.gov/colorectalcancer.html
• NHS — Bowel cancer: https://www.nhs.uk/conditions/bowel-cancer/
• National Cancer Institute — Colorectal Cancer: https://www.cancer.gov/types/colorectal
• WHO — Colorectal cancer fact sheet: https://www.who.int/news-room/fact-sheets/detail/colorectal-cancer

Frequently Asked Questions

What is the difference between colon cancer and colorectal cancer?

Colorectal is the umbrella term. Cancer starting in the colon is colon cancer, cancer starting in the last section is rectal cancer, and together they are grouped as colorectal cancer because they are investigated and often treated in similar ways.

Do all colon polyps turn into cancer?

No. Most polyps never become cancer. One family, adenomas, can change slowly over years, which is why polyps found during colonoscopy are usually removed and examined — you cannot reliably tell the type just by looking.

What symptoms should prompt a prompt medical assessment?

A lasting change in bowel habit, blood in or on the stool, ongoing abdominal discomfort, unexplained weight loss, or persistent unexplained tiredness. Each has many more common causes than cancer, but each deserves assessment by your own clinician.

How is colorectal cancer diagnosed for certain?

Only tissue examination confirms it. Biopsies or a removed polyp are examined under a microscope by a pathologist; scans and blood tests then help stage the cancer and plan treatment, but they do not replace the tissue diagnosis.

Is a stoma always needed after bowel cancer surgery?

No. Many operations rejoin the bowel without a stoma. Whether one is needed — temporarily or permanently — depends on the cancer's position and the operation required, and your surgeon should discuss it with you beforehand.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about colorectal cancer, not medical advice and not a diagnosis. Decisions about screening, investigation and treatment belong with your own clinical and oncology team, who can examine you and review your results.