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Colorectal Cancer: Why Bowel Symptoms Should Never Be Ignored

  • Prof. Dr. Zahid Mahmood
  • August 4, 2026

Colorectal Cancer: Why Bowel Symptoms Should Never Be Ignored

By Prof. Dr. Zahid Mahmood — General, Laparoscopic & Laser Surgeon, Lahore

Colorectal cancer — cancer of the colon or rectum — is one of the most common cancers I treat, and also one of the most preventable and, when caught early, most curable. The frustrating reality I see in clinic is that many patients delay seeking help for weeks or months because bowel symptoms feel embarrassing to discuss, or because they assume bleeding or a change in bowel habit is “just piles.” That delay matters enormously, because the single biggest factor determining whether this cancer can be cured is how early it is found. This article explains how colorectal cancer develops, who is at higher risk, the symptoms that deserve prompt attention, and what modern treatment actually involves.

How colorectal cancer develops

The great majority of colorectal cancers do not appear suddenly — they develop slowly, over years, from small, initially harmless growths on the lining of the bowel called polyps. Most polyps never become cancerous, but certain types, particularly larger ones or those with specific microscopic features, can gradually accumulate genetic changes that allow them to become invasive cancer. This is called the adenoma-to-carcinoma sequence, and it’s the reason colonoscopy — which allows a doctor to find and remove polyps before they ever become cancer — is one of the most genuinely effective cancer-prevention tools in medicine. It also explains why colorectal cancer is so often curable when caught early: it typically starts as a slow, local process before it spreads.

Who is at higher risk

Colorectal cancer becomes significantly more common from the age of 50 onward, and most cases are diagnosed in patients in their sixties, seventies, and beyond. But age is only one factor. A diet consistently high in red and processed meat and low in fibre is associated with a higher risk, as are smoking and heavy alcohol use. Long-standing inflammatory bowel disease, such as ulcerative colitis, also raises risk over time. Family history matters a great deal — if a first-degree relative (parent, sibling, or child) developed colorectal cancer before the age of 50, this can point toward one of several inherited colorectal cancer syndromes, and is worth mentioning specifically to your doctor, since it may change how early and how often you should be screened. On the protective side, dietary fibre, regular physical activity, and — under medical guidance — long-term low-dose aspirin in appropriate individuals have all been associated with reduced risk.

When it runs strongly in a family

A small proportion of colorectal cancers — but an important one to recognise — arise because of an inherited genetic condition rather than the more common combination of age, lifestyle, and chance. Lynch syndrome is the most common of these, an inherited fault that substantially raises lifetime colorectal cancer risk and typically causes cancer at a younger age than usual; families affected often see colorectal, womb, or other cancers appearing across multiple generations and before age 50. A rarer but more dramatic condition, familial adenomatous polyposis, causes hundreds to thousands of polyps to develop throughout the colon from adolescence onward, with a near-certain risk of cancer if the colon isn’t removed proactively. Neither condition is common, but if your family history includes several relatives with colorectal or related cancers, particularly at a younger age, this is worth a specific conversation with your doctor about genetic counselling and earlier, more frequent surveillance — for these families, colonoscopy screening often needs to start decades earlier than the general population’s age-50 guideline.

The symptoms that deserve prompt attention

Where the cancer sits in the bowel genuinely changes how it tends to present, and understanding this helps explain why some cases are caught late.

Cancers on the left side of the colon and in the rectum most often cause a change in bowel habit — new or worsening constipation, looser stools, or an altered pattern that persists for several weeks — along with rectal bleeding, which patients understandably often assume is from haemorrhoids. This assumption is exactly what delays diagnosis: bleeding from piles is extremely common and usually harmless, but bleeding is also the single most common symptom of a left-sided colorectal cancer, and the two cannot be reliably told apart without a proper examination.

Cancers on the right side of the colon behave differently and are, in some ways, more dangerous simply because they hide better. Rather than bleeding visibly or changing bowel habit early on, they tend to bleed slowly and internally, often presenting only as unexplained iron-deficiency anaemia — tiredness, breathlessness, or pallor discovered on a routine blood test — or as an abdominal mass, sometimes without any bowel symptoms at all until the disease is more advanced.

A meaningful proportion of patients — around one in five — first present as an emergency, with the bowel obstructed, bleeding heavily, or occasionally perforated, and outcomes in this situation are measurably worse than for patients diagnosed through planned assessment, even at the same cancer stage. This is one of the strongest arguments for taking early, non-emergency symptoms seriously rather than waiting for them to become severe.

Why screening matters so much

Colorectal cancer is particularly well suited to screening, because the prognosis improves dramatically the earlier it is caught, and because screening can prevent the cancer altogether by finding and removing polyps before they ever turn malignant. The modern screening test used in most structured programmes is a simple, private, at-home stool test called a faecal immunochemical test (FIT), which detects tiny amounts of blood in the stool not visible to the naked eye. It’s more accurate and considerably easier to use than the older stool tests, and a positive result leads on to a colonoscopy for a definitive look. For patients without a structured local screening programme available to them, I would still recommend a conversation with a doctor about baseline screening once past the age of 50 — or earlier, with a significant family history — rather than waiting for symptoms to appear.

How we investigate someone with symptoms

For a patient presenting with rectal bleeding or a change in bowel habit, a flexible sigmoidoscopy or full colonoscopy is the key investigation — a camera examination that allows direct visualisation of the bowel lining, biopsy of anything suspicious, and, very usefully, removal of polyps in the same sitting before they can progress. If a cancer is found or strongly suspected, staging scans follow — typically a CT scan of the chest, abdomen, and pelvis to check whether the disease has spread beyond the bowel, and for rectal cancers specifically, an MRI to assess the local extent of the tumour with the detail needed to plan surgery precisely.

Understanding staging, in plain terms

Doctors describe how advanced a colorectal cancer is using a staging system, and while the terminology (Dukes’ stages A–C, or the more detailed modern TNM system) can sound intimidating, the underlying idea is simple and directly tied to prognosis:

  • Earliest stage — the cancer is confined to the wall of the bowel itself, without spreading through it or to lymph nodes. This stage has an excellent outlook, with around 95% of patients disease-free five years after surgery alone.
  • Locally advanced — the cancer has grown through the full thickness of the bowel wall but still hasn’t reached the lymph nodes. Five-year disease-free survival with surgery alone is still good, at around 85%.
  • Lymph node involvement — cancer cells have reached the nearby lymph nodes. This roughly halves the five-year disease-free survival compared to earlier stages with surgery alone, which is exactly why chemotherapy after surgery becomes strongly recommended at this stage — it meaningfully improves those odds.
  • Metastatic disease — the cancer has spread to a distant organ, most commonly the liver, and less often the lungs. This is the most serious stage, but importantly, it is not automatically untreatable — see below.

The single clearest message from these numbers is this: stage at diagnosis is the single biggest factor in outcome, and stage at diagnosis is, in turn, heavily influenced by how quickly symptoms are investigated.

Treatment: surgery is the foundation

For the majority of colorectal cancers, surgical removal of the affected segment of bowel, along with its draining lymph nodes and blood supply, is the cornerstone of curative treatment. The specific operation depends on where the tumour sits — a right hemicolectomy removes the right side of the colon for cancers of the caecum or ascending colon, a left hemicolectomy for cancers of the descending or sigmoid colon, and rectal cancers have their own specific surgical approaches, often combined with radiotherapy beforehand (covered in more detail in a separate article on rectal cancer specifically).

Laparoscopic (keyhole) surgery is now well established for colon cancer, with outcomes and cancer clearance equivalent to open surgery, but with less blood loss, lower wound infection rates, and a faster recovery — this is my preferred approach wherever a patient is a suitable candidate. Modern recovery protocols (often called ERAS — enhanced recovery after surgery) combine several small measures, from careful anaesthesia to very early mobilisation and early return to eating, and have reduced typical hospital stays after colon surgery from ten to fourteen days down to as little as three to five days for many patients.

When a patient presents as an emergency — with obstruction, bleeding, or perforation — the approach is more individualised. A right-sided obstructing cancer can usually still be resected and joined back together in one operation. A left-sided obstruction sometimes needs a temporary stoma, or in select cases, a metal stent can be placed endoscopically to relieve the blockage first, turning an emergency operation into a planned one days or weeks later with a much lower chance of ending up with a stoma.

What to expect after surgery

Most patients are encouraged to sit up, start sipping fluids, and begin gently walking within a day of surgery, which sounds surprising to many but is genuinely one of the most important things that speeds recovery and reduces complications. Diet is advanced as tolerated over the following days rather than delayed, and with modern recovery protocols, many patients who have had keyhole surgery for colon cancer go home within three to five days. Some patients — particularly those having rectal surgery low in the pelvis, or emergency surgery — may need a temporary stoma (an opening of the bowel onto the abdominal wall, with output collected in a bag) to allow a lower join to heal safely; this is planned and discussed in advance wherever possible, and is very often reversed with a second, smaller operation once healing is confirmed. Regular follow-up afterward — clinical review, blood tests, and periodic scans or colonoscopy — continues for several years, since this is when any recurrence is most likely to be caught early and treated effectively if it does occur.

When chemotherapy is added

Not every patient needs chemotherapy after surgery. For early-stage disease confined to the bowel wall, surgery alone is usually curative, and chemotherapy adds little additional benefit. Once lymph nodes are involved, however, chemotherapy after surgery meaningfully improves the chance of long-term cure — commonly adding around 20 percentage points to five-year disease-free survival in that group. For some higher-risk earlier-stage cases, chemotherapy is still considered on an individual basis after multidisciplinary discussion.

Metastatic disease is not automatically the end of the road

I want to be honest but also genuinely encouraging on this point, because many patients assume a diagnosis of spread automatically means the disease is untreatable. That is not always true. When colorectal cancer has spread only to the liver, or only to the lungs, and the metastases are limited in number and location, surgical removal of those metastases — sometimes combined with chemotherapy before or after — can still achieve long-term, sometimes durable, disease control, with roughly 4 in 10 patients who undergo resectable metastasis surgery surviving five years or more. Even for patients with more widespread disease where surgery isn’t an option, modern chemotherapy and increasingly targeted drugs (based on the tumour’s specific genetic features) have meaningfully extended both survival and quality of life compared to a generation ago. Every case in this category deserves discussion by a multidisciplinary cancer team before being labelled untreatable.

What actually lowers your risk

While no lifestyle change eliminates risk entirely, a few genuinely evidence-based habits meaningfully shift the odds in your favour: a diet built around fibre-rich vegetables, fruit, and whole grains rather than red and processed meat; regular physical activity; maintaining a healthy weight; moderating alcohol; and not smoking. For selected individuals, particularly those with additional risk factors, a doctor may discuss long-term low-dose aspirin as a further risk-reducing option — this isn’t right for everyone, since aspirin carries its own risks such as bleeding, so it’s a decision made individually rather than a blanket recommendation. None of this replaces screening or prompt attention to symptoms, but together with those two, it represents genuinely meaningful, evidence-based prevention rather than folklore.

Warning signs worth getting checked

  • A change in bowel habit — looser stools, new constipation, or a different pattern — lasting more than a few weeks
  • Rectal bleeding, even if you assume it’s from piles
  • Unexplained tiredness, breathlessness, or pallor (possible anaemia)
  • Unexplained weight loss
  • A lump or mass felt in the abdomen
  • A persistent feeling of incomplete bowel emptying
  • A first-degree relative diagnosed with colorectal cancer before age 50 — worth raising proactively, even without symptoms

What you should do

If you’re over 50, please don’t wait for symptoms — ask about screening. If you have any of the symptoms above, particularly rectal bleeding or a genuine change in bowel habit lasting several weeks, get it properly assessed rather than assuming it’s haemorrhoids or something minor — the two can look identical to the patient and only an examination can reliably tell them apart. Early investigation is quick, usually straightforward, and is, without exaggeration, the single biggest thing within your control that determines the outcome if cancer is found.

To book a consultation with Prof. Dr. Zahid Mahmood, call 0300 413 0159 or visit professorzahid.com.

This article is for general awareness and does not replace a personal medical consultation.

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