Colon cancer symptoms, screening and what to do next
A clear, practical guide to the warning signs, when to get screened, and what actually happens if something is found.
Summary
Colon cancer, part of the broader group called colorectal cancer, often develops silently for years before it causes any obvious symptoms. This guide covers the warning signs worth taking seriously, why the disease is rising sharply in younger adults, when screening should actually start, and what practical steps to take next if you’re worried or if a screening test comes back abnormal.
This content is for informational purposes only and does not constitute medical advice. Many of the symptoms described here have common, non-cancerous causes. Always consult a qualified doctor for evaluation, diagnosis, and treatment specific to your situation. As of 2026.
Colon cancer has a reputation as an older person’s disease, and for a long time that was largely true. That’s changing quickly, and not in a good way. Rates in adults under 50 have been climbing for three decades, and colorectal cancer is now the leading cause of cancer death in men under 50 in the United States, and the second leading cause in women under 50. The reasons for that shift aren’t fully understood yet, but the practical takeaway is simple. This isn’t a disease you can safely assume you’re too young for.
This guide is built to help you recognise what actually matters, and know what to do about it.
What are the early symptoms of colon cancer?
Early colon cancer often causes no symptoms at all, which is exactly why screening matters so much. When symptoms do appear, a handful come up again and again.
- A change in bowel habits, diarrhoea, constipation, or narrower stools that lasts more than a few days.
- Blood in the stool, or on toilet paper, ranging from bright red to dark and tarry.
- A feeling that your bowel hasn’t fully emptied, even right after a bowel movement.
- Ongoing abdominal pain, cramping, or bloating that doesn’t resolve.
- Unexplained fatigue or weakness, which can come from anaemia caused by slow, hidden blood loss.
- Unintentional weight loss.
None of these symptoms is unique to colon cancer. Each one of them is far more commonly caused by something else entirely: haemorrhoids, irritable bowel syndrome, an infection, or a dietary change. That’s what makes them easy to dismiss, and it’s also why persistence matters most. A symptom that shows up once and disappears is different from one that lingers for weeks. The American Cancer Society’s full symptom list is a useful reference if you want to check something specific.
Why do so many people miss these symptoms?
Partly because the symptoms overlap so heavily with common, harmless conditions, and partly because talking about bowel habits still makes people uncomfortable enough to put off a conversation they’d have quickly about almost anything else.
There’s a second, more specific reason worth naming directly. Unexplained iron-deficiency anaemia, showing up as fatigue, weakness, or shortness of breath on a routine blood test, is one of the more overlooked warning signs. It doesn’t announce itself as a digestive symptom, and it’s sometimes chalked up to diet or a busy schedule rather than investigated further. If a blood test shows unexplained anaemia and it doesn’t resolve with an obvious explanation, that’s a reasonable moment to ask directly whether a colonoscopy is warranted.
What causes colon cancer?
Most colon cancer starts as a polyp, a small growth on the inner lining of the colon that is not initially cancerous. Over years, some polyps accumulate genetic changes that allow them to become cancerous. This slow progression is actually good news, because it creates a genuine window for screening to catch and remove polyps before they ever turn into cancer.
Several factors raise the likelihood of this happening.
- Age, with risk rising steadily after 45, though it’s increasingly showing up younger.
- A personal or family history of colorectal polyps or cancer.
- Inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease.
- Inherited conditions such as Lynch syndrome or familial adenomatous polyposis.
- Diets low in fibre and high in red or processed meat.
- Obesity, physical inactivity, smoking, and heavy alcohol use.
- Type 2 diabetes.
Having one or more of these factors doesn’t guarantee colon cancer will develop, and plenty of people diagnosed have no clear risk factor beyond age. But several of these, diet, activity level, smoking, and alcohol, are genuinely modifiable, which is part of why colon cancer is considered one of the more preventable cancers overall.
Why is colon cancer rising in younger people, in India and everywhere else?
This trend is real, global, and still not fully explained. In the United States, about 1 in 5 colorectal cancer cases is now diagnosed in someone under 54, compared with roughly 1 in 10 three decades ago. Researchers suspect diet, physical inactivity, obesity, and other environmental exposures play a role, but no single cause has been confirmed.
India shows a similar pattern, with a few distinct features worth knowing. Colorectal cancer is now the fourth most common cancer among men in India, and incidence has been climbing across nearly every Indian cancer registry, according to a review in the Indian Journal of Cancer. The average age at diagnosis in India tends to be younger than in Western countries, with some tertiary centre studies reporting a mean age around 47, and up to a third of cases occurring before age 40. Indian studies specifically looking at young-onset colorectal cancer have found these cases are more likely to present at an advanced stage and more likely to involve an aggressive histological subtype called signet-ring cell carcinoma.
The presentation pattern in India is also skewed later than ideal. In one Indian dataset, only about 4% of cases were caught at Stage I, while over a quarter were already Stage IV at diagnosis. That gap between what’s possible with early detection and what’s actually happening on the ground is really the central problem this guide is trying to address.
When should you start colon cancer screening?
Situation | Recommended approach |
Average risk, United States guidelines (ACS, USPSTF) | Begin screening at age 45 and continue through 75. |
Average risk, India | No formal national screening guideline currently exists. Experts increasingly recommend discussing screening with a doctor from around 45, especially in urban settings with rising incidence. |
Family history of colorectal cancer or polyps | Often recommended to start earlier, sometimes 10 years before the age the relative was diagnosed. Discuss timing directly with your doctor. |
Inflammatory bowel disease or a known genetic syndrome | Screening typically starts earlier and happens more frequently. Plan this with a specialist. |
It’s worth being direct about something here. India doesn’t yet have a unified, national colorectal cancer screening guideline the way the United States does. Several Indian medical bodies have called for one given the rising incidence, but until that exists, the practical approach is a personal conversation with a doctor, particularly from your mid-40s onward, or earlier with any family history or persistent symptoms.
What are the screening tests available?
Screening broadly falls into two categories: tests that look directly at the colon, and tests that check a stool sample for hidden signs of blood or abnormal cells.
Colonoscopy is the most thorough option, allowing a doctor to examine the entire colon and remove polyps in the same procedure, before they ever have the chance to become cancerous. It’s typically repeated every 10 years for average-risk people with a normal result.
Faecal immunochemical testing (FIT) is a simple, non-invasive stool test that checks for hidden blood, done annually. It has a reported sensitivity around 97% and a negative predictive value near 99.8%, making it a genuinely useful, low-cost triage tool, particularly relevant in settings where colonoscopy access is limited.
Flexible sigmoidoscopy examines the lower part of the colon and is sometimes used alongside stool-based testing, though it’s less commonly used as a standalone option than it once was.
CT colonography, a specialised imaging scan, is an alternative for people who can’t or prefer not to have a standard colonoscopy.
No single test is automatically the right choice for everyone. The right one depends on personal risk, access, and what a doctor recommends based on your specific situation.
Our guide on cancer diagnostics and early detection covers how these tests fit into the bigger picture of early cancer detection.
What happens if something is found.
If a screening test finds a polyp or something abnormal, the next step is almost always a colonoscopy, if one hasn’t already been done, since it allows both diagnosis and, for most polyps, immediate removal in the same procedure.
If a biopsy confirms cancer, the next step is staging, determining how far, if at all, the cancer has spread beyond the colon wall. This most directly shapes the treatment plan and outlook. The difference staging makes is substantial. Localised colon cancer, caught before it has spread beyond the colon, has a 5-year relative survival rate of around 90%, according to NCI SEER data. Once it has spread to distant organs, that figure drops to roughly 15%. That gap is really the entire argument for screening in one statistic.
If you’ve already received a diagnosis and want a second set of eyes on the plan, our second opinion page explains how that process works.
How is colon cancer treated?
Treatment depends heavily on the stage at diagnosis, and it’s rarely just one approach.
Surgery to remove the cancerous section of the colon is the primary treatment for most non-metastatic colon cancer, and is often curative on its own for early-stage disease.
Chemotherapy is commonly added after surgery for higher-risk or more advanced stages, to reduce the chance of recurrence, and is central to treatment once the cancer has spread. Our chemotherapy page explains how this works in more detail.
Targeted therapy and immunotherapy are used for select advanced or metastatic cases, often guided by molecular testing of the tumour to identify which specific drugs are likely to work. See our pages on targeted therapy and immunotherapy for more on how each approach is used.
Radiation therapy plays a larger role in rectal cancer specifically than in colon cancer higher up the digestive tract, often combined with chemotherapy before surgery.
The right combination depends entirely on stage, tumour location, and, increasingly, the specific molecular profile of the tumour, which is why an individualised treatment plan matters more than a generic protocol.
What should you actually do next?
If you have a persistent symptom from the list above, don’t wait it out hoping it resolves on its own. See a doctor, describe exactly what’s happening and for how long, and let them guide the next step, whether that’s further testing or simple reassurance.
If you’re over 45, or have a family history, and haven’t had a screening conversation with a doctor yet, that conversation itself is the next step, not a full colonoscopy on day one. A doctor can help you weigh options, including FIT testing as a lower-barrier starting point.
If a screening test has already come back abnormal, follow through with the recommended next test rather than sitting on the result. The entire value of screening depends on acting on what it finds.
The takeaway
Colon cancer is genuinely one of the more preventable and treatable cancers, but only when it’s caught before it has had time to spread. Persistent symptoms deserve a proper look rather than an assumption, and given how much earlier this disease is now showing up, screening conversations shouldn’t wait for a specific trigger.
Book a consultation with Dr Aditya Sarin at Sir Ganga Ram Hospital, New Delhi