Colonoscopy — Endoscopic bowel examination

A colonoscopy is a specialised endoscopic procedure designed to inspect the entire mucosal surface of the colon and rectum. During the test, a long, slender, flexible tube called a colonoscope is gently advanced through the anus into the bowel. The instrument incorporates a light source, a digital video camera, and working channels that permit the passage of miniature surgical tools.

Clinicians use these instruments to identify mucosal inflammation, ulceration, bleeding sites, and abnormal tissue growths known as polyps. If suspicious lesions or polyps are found, the operator can excise them immediately or obtain small tissue samples, known as biopsies. These specimens are subsequently transferred to a pathology laboratory for histological evaluation to determine whether pre-cancerous or malignant cells are present.

A colonoscopy plays a vital role in both preventing and diagnosing bowel cancer. Many colorectal cancers develop slowly from benign polyps; identifying and removing these polyps during an examination stops cancer before it starts. For individuals experiencing symptoms like persistent bowel habit changes or rectal bleeding, the procedure offers definitive answers. Knowing whether a growth is present allows the multidisciplinary oncology team to formulate an accurate, tailored treatment plan quickly, avoiding unnecessary delays in care.

A colonoscopy is often arranged after an abnormal screening test, such as a faecal immunochemical test (FIT) detecting occult blood. Tissue biopsies collected during the procedure undergo histological examination. Pathologists assess these samples for molecular biomarkers, including microsatellite instability (MSI), mismatch repair (MMR) protein status, and mutations in genes such as KRAS, NRAS, and BRAF, which guide future systemic therapies.

This procedure is primarily associated with colorectal cancer, which encompasses colon cancer and rectal cancer. It is also utilised to monitor patients with hereditary cancer conditions, such as Lynch syndrome and familial adenomatous polyposis, who carry a significantly higher risk of bowel malignancies. In addition, it helps assess neuroendocrine tumours of the lower digestive tract and evaluates gastrointestinal lymphomas.

The findings directly influence management pathways. Small, early malignant lesions confined to polyps may be completely excised endoscopically, potentially sparing the patient major surgery. If an invasive tumour is diagnosed, staging scans follow, and the team will plan surgical resection, such as a colectomy. Biopsy results also dictate eligibility for neoadjuvant chemotherapy, radiotherapy, or targeted immunotherapy regimens.