Synopsis
Recognise symptomatic and screen-detected colorectal cancer, use FIT without delaying red-flag assessment, obtain complete colonoscopic histology and site-specific staging and coordinate endoscopic, surgical, radiation, systemic, genetic and survivorship care.
- Right-sided cancer commonly produces iron-deficiency anaemia, fatigue and vague pain; left-sided disease more often causes altered habit and obstruction, and rectal cancer causes bleeding, urgency and tenesmus.
- Use quantitative FIT to triage appropriate symptomatic patients, but a low result does not overrule a rectal or abdominal mass, persistent unexplained symptoms, iron deficiency or strong clinical concern.
- The diagnostic reference standard is complete colonoscopy with biopsy, careful lesion localisation and assessment for synchronous neoplasia; CT colonography is the principal alternative when colonoscopy is incomplete or unsuitable.
- Obtain contrast CT chest, abdomen and pelvis for distant staging. For rectal cancer, high-resolution MRI pelvis is the reference local staging test and should report mesorectal fascia, nodes, extramural vascular invasion and sphincter anatomy.
- Measure baseline CEA for prognosis and later surveillance, but do not use a normal CEA to exclude cancer or a raised value without imaging to diagnose recurrence.
- Test every newly diagnosed colorectal cancer for mismatch-repair deficiency or microsatellite instability to screen for Lynch syndrome and inform prognosis and advanced immune treatment.
- Selected en-bloc endoscopically removed T1 cancer with favourable depth, differentiation, lymphovascular, budding and margin features may be cured without segmental surgery after expert pathology review.
- Colon cancer treatment is oncological segmental resection with intact mesocolic planes and adequate nodes, followed by adjuvant chemotherapy for stage III and selected high-risk stage II disease.
- Rectal treatment is MRI risk adapted: early disease may undergo local or total mesorectal excision, while threatened margins or higher-risk disease may need neoadjuvant radiotherapy, chemoradiation or total neoadjuvant therapy.
- A complete clinical response after rectal neoadjuvant therapy can enter watch-and-wait only within a specialist programme with intensive examination, endoscopy and MRI; it is not no follow-up.
- Metastatic liver or lung disease may still be curable through resection or ablation after hepatobiliary or thoracic MDT review; do not call all stage IV disease permanently unresectable.
- Advanced systemic therapy uses RAS, BRAF, MMR or MSI and selected HER2 and other markers, tumour side, performance and prior treatment to choose targeted and immune options.
- Stoma siting and counselling, fertility and sexual function, prehabilitation, nutrition and enhanced recovery begin before treatment and continue into surveillance.
Key red flags
Peritonism, fever, shock, free air or rapidly worsening abdominal pain suggests perforated cancer and needs emergency surgery and antibiotics.
Absolute constipation, distension, colicky pain, vomiting or an incompetent ileocaecal valve with caecal dilatation suggests threatened large-bowel obstruction.
Persistent rectal bleeding, iron-deficiency anaemia, unexplained weight loss or altered bowel habit requires a colorectal pathway even when haemorrhoids are present.
A palpable rectal or abdominal mass, supraclavicular node, hepatomegaly, ascites or obstructive jaundice suggests advanced disease.
New back pain, leg weakness, perineal sensory change or bladder dysfunction with pelvic recurrence raises neural or spinal compression.
Fever or severe diarrhoea during chemotherapy may indicate neutropenic sepsis, enterocolitis or immune colitis and requires urgent acute-oncology assessment.
Absolute constipation, marked distension, faeculent vomiting, peritonism, sepsis or free air requires urgent CT and colorectal surgical care.
Investigation priorities
Measure faecal haemoglobin to prioritise colorectal investigation in adults with compatible lower-GI symptoms.
Stage liver, lung, peritoneal, nodal and locally invasive disease and identify potentially resectable metastases.
Management branches
An adult has rectal bleeding, altered bowel habit, iron deficiency, weight loss or compatible abdominal symptoms.
- Assess haemodynamic state, obstruction, abdominal and rectal masses and full-blood-count evidence of iron deficiency, activating emergency care when unstable.
- Request quantitative FIT where appropriate and refer at the current threshold, but refer or investigate persistent red flags and masses regardless of a low result.
- Complete colonoscopy and biopsy or CT colonography with a route to tissue, then communicate diagnosis and obtain site-specific staging through the colorectal MDT.