investigations in colorectal cancer

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In patients with suspected colorectal cancer, appropriate investigations should be carried out promptly without any delay (1).

Three methods have been shown to be effective in the primary diagnosis of colorectal cancer:

  • colonoscopy
    • for many years this has been regarded as the reference standard for diagnosing
    • is known to have high sensitivity and specificity for detection of cancer, pre-malignant adenomas and other symptomatic colonic diseases
    • offered to patients without any major co-morbidity (e.g. serious cardiorespiratory or neurological co-morbidity)
    • it also has the advantage of obtaining a biopsy (unless contraindicated)from any suspected lesion and also complete removal of most benign lesions during the same procedure
  • barium enema/flexible sigmoidoscopy
    • due to limited published evidence of the diagnostic accuracy of barium enema (and concerns with sensitivity when compared to colonoscopy) the combined investigation pathway of flexible sigmoidoscopy followed by barium enema is  offered to patients in many centres
    • is offered to  patients with major co-morbidity
  • CT colonography
    • can be used as a sensitive and safe alternative to colonoscopy (if the local radiology service can demonstrate competency in this technique)
    • is substantially less invasive than colonoscopy and does not require patient sedation
    • offer a colonoscopy with biopsy in cases with lesions suspicious of cancer to confirm the diagnosis (2)

Staging of colorectal cancer (1)

  • contrast-enhanced computed tomography (CT) of the chest, abdomen and pelvis, should be offered to estimate the stage of disease, to all patients diagnosed with colorectal cancer unless it is contraindicated. No further routine imaging is needed for patients with colon cancer
  • magnetic resonance imaging (MRI) to assess the risk of local recurrence, as determined by anticipated resection margin, tumour and lymph node staging, should be offered to all patients with rectal cancer unless it is contraindicated

Follow-up after apparently curative resection

  • regular surveillance with:
    • a minimum of two CTs of the chest, abdomen, and pelvis in the first 3 years and
    • regular serum carcinoembryonic antigen tests (at least every 6 months in the first 3 years)

Molecular biomarkers to guide systemic anti-cancer therapy (3)

  • test for RAS and BRAF V600E mutations in all people with metastatic colorectal cancer suitable for systemic anti-cancer treatment


  • patients should be informed that more than one investigation may be necessary to confirm or exclude the diagnosis of colorectal cancer (2)


Last edited 02/2020 and last reviewed 05/2022