Colorectal cancer

The Surgeon's Guide to Bowel Cancer: Diagnosis, Staging and Advanced Treatment

Bowel cancer (also known as colorectal cancer) is the collective term for cancer in the colon and rectum. The diagnosis is serious. Work-up and treatment today are organised in multidisciplinary pathways involving surgery, oncological treatment and assessment of the tumour biology.

The Danish Health Authority's cancer pathway for colorectal cancer (2022) states about 4,000 new cases a year in Denmark (Danish Health Authority). The Danish organised screening programme starts with a FIT stool test every two years for people aged 50-74. If the FIT is positive, colonoscopy is offered, and colonoscopy is also used diagnostically where there is relevant suspicion or symptoms.

FIT is a triage and prioritisation tool, not a diagnosis and not a universal rule-out test. In people with symptoms it helps prioritise investigation, and a low or negative FIT cannot on its own withhold referral. Persistent or unexplained symptoms, ongoing clinical concern, iron deficiency anaemia, persistent or recurrent rectal bleeding, a palpable mass or suspected obstruction all require clinical assessment with safety-netting and referral through the current Danish pathway. The joint ACPGBI and BSG guideline uses a threshold of 10 µg Hb/g faeces in primary care and states that patients should not be excluded from referral on the basis of FIT alone (Gut 2022;71:1939-1962). That threshold comes from a UK context, and local Danish pathways may differ.

Why does bowel cancer occur? From polyp to cancer

Some cases of bowel cancer develop from precursor lesions in the bowel lining, typically polyps such as adenomas or serrated lesions. Not all polyps turn into cancer, and not every cancer follows the same route.

Normally cells only divide when needed, but if the control mechanisms fail, the mucosal cells grow uncontrollably. Over time, some of these polyps (specifically adenomas) can become autonomous and develop into cancer. The process typically takes several years.

Removing precursor lesions at colonoscopy is a well-documented part of prevention. When and how often colonoscopy is relevant depends on the individual findings, age and risk profile.

Symptoms: When should you see a doctor?

The symptoms of colon and rectal cancer vary, but you should always see a doctor as soon as possible if you notice any of the following:

Bleeding and anaemia

• Blood in the stool or on the toilet paper: Bleeding is often mistaken for haemorrhoids but can be a sign of cancer. Read more about rectal bleeding.
• Unexplained anaemia: Prolonged, hidden bleeding from the bowel can lead to anaemia, which shows up as fatigue and pale skin. Minor bleeding can be detected by a stool test for blood.

Changes in bowel function

• Changes in stool: Altered frequency, consistency or noticeably thinner calibre of the stool over weeks.
• A feeling of incomplete emptying after passing stool (typical of rectal cancer).

Bowel obstruction

If the tumour grows large enough, it can fully or partially block the bowel (obstruction), which can cause:

• A distended, bloated abdomen.
• Unexplained weight loss, nausea and vomiting.
• Abdominal pain (rarely in early colon cancer).
• Rectal pain (seen mainly when rectal cancer grows into surrounding tissue).

If bowel obstruction is suspected, contact 1813 in the Capital Region or your local out-of-hours medical service immediately: a severely distended and painful abdomen, complete stop of passing gas or stool, persistent vomiting, or feeling generally unwell. Call 112 in a life-threatening situation, with severely impaired general condition, reduced consciousness, circulatory or breathing problems, or if safe transport is not possible. A scheduled appointment at a specialist clinic is not an alternative.

Diagnosis: How is bowel cancer diagnosed?

To diagnose bowel cancer and plan the right treatment, you go through a series of specialised examinations:

1. Initial examination: The doctor inserts a finger into the rectum (digital rectal exam) to feel for lumps in the lower part.
2. Endoscopy (colonoscopy): The examination usually chosen for direct assessment of the bowel, because tissue samples can be taken and polyps removed during the same procedure. A flexible tube is passed through the anus. Whether the whole colon and rectum can be assessed depends on the quality of the bowel preparation and on whether the examination can be completed. See the other endoscopic examinations offered at the clinic.
3. Microscopy of tissue samples: If cancer is suspected during colonoscopy, tissue samples will be taken for microscopic examination. The samples are examined for cell changes and various markers, including MMR status (Mismatch Repair). MMR status is used among other things to assess possible Lynch syndrome, to provide prognostic information, and as part of the basis for treatment choice in selected disease stages. MMR status alone does not determine the medical treatment.
4. CT colonography ("virtual colonoscopy"): According to the 2020 ESGE/ESGAR guideline, CT colonography is the radiological examination of choice for colorectal neoplasia and is recommended after an incomplete colonoscopy, preferably on the same or the next day following multidisciplinary assessment (ESGE/ESGAR 2020). CT colonography and colonoscopy have different capabilities: biopsies cannot be taken and polyps cannot be removed at CT colonography, so a relevant finding may require a subsequent colonoscopy.
5. Staging (scans): If cancer is found, it is investigated for possible spread using:
   • CT scan of the chest and abdomen.
   • MRI and/or ultrasound through the rectum (specifically for rectal cancer, to assess local extent).

Disease stages: TNM classification

For treatment planning and prognostic assessment, bowel cancer is divided into stages using the international TNM system, which describes the extent of the disease. Staging is one of several factors considered when treatment is decided in a multidisciplinary team:

• T (Tumour): Local growth of the tumour (T1-T2 are limited to the bowel wall; T3-T4 have grown deeper or through the bowel wall).
• N (Node): Whether the cancer has spread to nearby lymph nodes (N0 means no spread; N1-N2 means spread to lymph nodes).
• M (Metastasis): Whether there is spread to other organs, for example the liver or lungs (M0 means no distant spread; M1 means spread).

The four cancer stages

Stage	TNM criteria	Description and prognosis
Stage 1	T1-2, N0, M0	Small tumour, no spread to lymph nodes or other organs. Stage describes groups, not an individual prognosis.
Stage 2	T3-4, N0, M0	Larger tumour, but still no spread to lymph nodes or other organs.
Stage 3	T1-4, N1-2, M0	The cancer has spread to local lymph nodes, but there is no distant spread.
Stage 4	Any T, any N, M1	Spread to other organs in the body (metastases).

The aim of treatment depends on the stage. When the disease has not spread, the aim is usually cure, whereas with widespread disease treatment may aim to slow the cancer and relieve symptoms. The aim is set individually at a multidisciplinary team meeting.

Treating bowel cancer: A tailored, multidisciplinary approach

Treatment is highly specialised and adapted to the individual patient in close cooperation between surgeons and oncologists.

Surgical treatment (operation)

Surgery remains the cornerstone of treatment. Most centres now offer keyhole surgery (laparoscopic or robot-assisted), where the surgeon operates through small incisions. This means less pain and faster recovery.

• Surgery for colon cancer: The cancer, a section of healthy bowel on either side and the surrounding fatty tissue with lymph nodes are removed. The bowel is usually joined back together immediately.
• Surgery for rectal cancer: All or large parts of the rectum are removed together with the surrounding fatty tissue (mesorectum) to reduce the risk of local recurrence.
  • Temporary stoma: Often created to protect the bowel join and let the bowel rest while it heals.
  • Permanent stoma: Necessary if the tumour sits so close to, or involves, the sphincter that the sphincter must be removed.

Medical and oncological treatment (before and after surgery)

Treatment is given either to support surgery, to shrink the tumour beforehand or as palliative care.

• Treatment BEFORE surgery (neoadjuvant treatment):
  • For rectal cancer, radiotherapy is used, often combined with chemotherapy, to shrink the tumour before surgery.
  • Following the latest guidelines, medical treatment (chemotherapy or targeted immunotherapy) is now also increasingly offered before surgery for colon cancer if the tumour is locally advanced or has specific genetic features (for example dMMR/MSI-high).
• Treatment AFTER surgery (adjuvant treatment): Chemotherapy may be offered after surgery (typically in stage 3 and in selected stage 2 cases after individual assessment at a multidisciplinary team meeting) to remove any microscopic cancer cells and reduce the risk of recurrence.

A modern option: "Watch and Wait" (organ-preserving strategy)

For a selected group of rectal cancer patients who receive intensive radio- and chemotherapy before the planned surgery, the tumour can sometimes disappear completely (complete clinical response). Following the latest guidelines, in these special cases, and under very close follow-up with scans, surgery can be postponed to preserve natural bowel function and avoid a stoma.

Prevention: Can I lower my risk?

Yes, there is a lot you can do yourself.

Taking part in the national screening programme for colon and rectal cancer (ages 50-74) reduces risk and mortality at population level. Investigating symptoms is a separate pathway in which colonoscopy may be relevant, as it may be when there are signs of hidden blood in the stool.

Beyond that, lifestyle plays a significant role:

Factors that INCREASE risk	Factors that DECREASE risk
Overweight and a high calorie intake	Regular physical activity (exercise)
High intake of red and processed meat	Plenty of fruit, vegetables and berries
High alcohol consumption	A fibre-rich diet (whole grains)
Smoking	Intake of fish and low-fat dairy

The prognosis

Survival for patients with bowel cancer depends among other things on the disease stage at diagnosis and on the biology of the tumour. Treatment is planned individually in a multidisciplinary setting.