01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Colorectal cancer may bleed intermittently, narrow the lumen, alter rectal capacity or cause chronic iron loss. Right-sided tumours more often present through occult blood loss or anaemia, while left-sided and rectal lesions more often alter stool passage, but location patterns overlap and cannot replace investigation.
Current UK assessment combines history, abdominal and rectal examination, full blood count and quantitative FIT for specified symptomatic adults. The referral route changes when a mass is palpable or obstruction, perforation or major bleeding is present, because urgent specialist or emergency care then takes precedence over routine triage.
Key points
- Rectal bleeding, persistent bowel-habit change, weight loss, abdominal pain and iron-deficiency anaemia can occur alone or together.
- Offer quantitative FIT for the adult symptom groups specified by NICE NG12 and record who will review the value.
- Refer on the suspected colorectal-cancer pathway when FIT is at least 10 micrograms haemoglobin per gram of faeces.
- Do not delay referral for a rectal mass, unexplained anal mass or anal ulceration while waiting for FIT.
- Vomiting, distension, absolute constipation, peritonism or shock suggests complicated cancer and requires emergency surgical assessment.
- Confirm that endoscopy or CT colonography, tissue diagnosis, staging and multidisciplinary review have named owners.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Sporadic adenoma-carcinoma sequence
Most cancers arise from acquired epithelial driver alterations within adenomatous or serrated precursor lesions; accumulated changes permit dysplasia, invasion and metastatic competence over time.
Inherited or inflammation-associated carcinogenesis
Lynch syndrome, polyposis syndromes and longstanding colonic inflammation create distinct mismatch-repair, polyposis or inflammation-driven pathways and can alter age, multiplicity and surveillance needs.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Mucosal invasion
Dysplastic epithelium breaches the muscularis mucosae and progresses through bowel wall, gaining access to lymphatic channels, regional nodes and blood vessels.
- 2Chronic tumour bleeding
Friable surface vessels leak intermittently; right-sided lesions may cause occult iron loss, whereas distal blood is more likely to remain visibly mixed with or coating stool.
- 3Luminal narrowing and obstruction
Circumferential growth and desmoplastic reaction restrict passage, causing altered calibre, proximal faecal loading and dilatation before ischaemia or perforation develops.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Ask about duration and progression of blood, stool-form change, urgency, tenesmus, pain, appetite and weight; intermittent symptoms do not make cancer benign.
Occult tumour bleeding may deplete iron before blood becomes visible, producing fatigue, dyspnoea, low ferritin and sometimes microcytosis.
A palpable mass materially raises cancer probability and should be described by site, mobility and examination limitations rather than softened by a low FIT.
Progressive distension, colic, vomiting, obstipation, peritonism or physiological compromise indicates a time-critical complication requiring surgical assessment.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Quantitative FITFirst step - Why
- Stratify symptomatic colorectal-cancer risk in the NICE pathway.
- Interpretation and limitations
- At least 10 micrograms haemoglobin per gram supports suspected-cancer referral; lower results require safety-netting against persistence and examination.
- 02
Full blood count and ferritin - Why
- Identify iron-deficiency anaemia and treatment-relevant severity.
- Interpretation and limitations
- Normal haemoglobin does not exclude cancer, while confirmed unexplained deficiency requires source investigation.
- 03
Digital rectal examination - Why
- Detect low rectal tumour, blood, melaena or another anorectal lesion.
- Interpretation and limitations
- A normal examination cannot exclude a higher rectal or colonic cancer because the finger has limited reach.
- 04
Colonoscopy or CT colonography with biopsy planning - Why
- Define and sample the suspected lesion.
- Interpretation and limitations
- Colonoscopy permits tissue and polypectomy; CT colonography may complete anatomy but suspicious findings still require histology.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Inflammatory bowel disease
Colitis can cause rectal blood, urgency, anaemia and weight loss; endoscopic distribution and histology distinguish active inflammation, dysplasia and invasive malignancy.
Benign anorectal disease
Haemorrhoids and fissure commonly cause fresh blood, but neither adequately explains an abdominal mass, progressive bowel-habit change, weight loss or unexplained iron deficiency.
Diverticular disease
Diverticular bleeding may be brisk and painless, while chronic diverticular inflammation can narrow the sigmoid; complete structural assessment and biopsy resolve uncertainty with cancer.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked case: above-threshold FIT with iron deficiencyMove from symptom triage to tissue diagnosis and stagingFirst stepA 63-year-old has eight weeks of looser stool, fatigue and intermittent blood mixed with stool. Examination finds no mass; haemoglobin is 108 g/L with ferritin 7 micrograms/L and FIT is 34 micrograms haemoglobin per gram.+
- 1Check observations and ask about heavy bleeding, vomiting, distension and passage of flatus; stable physiology and absence of obstruction allow an urgent outpatient pathway.
- 2Document the symptom duration, weight trend, family history and medicines, then complete abdominal and consented digital rectal examination without treating the normal examination as exclusion.
- 3Interpret the FIT of 34 as above the NICE threshold of 10 and submit a suspected colorectal-cancer referral that includes the numerical value and confirmed iron deficiency.
- 4Start iron replacement while investigation proceeds. Colonoscopy finds an ascending-colon mass and biopsy confirms adenocarcinoma; request CT staging rather than repeating FIT.
- 5Verify that histology and CT are reviewed at colorectal MDT and that the patient receives the recorded treatment decision and urgent advice for obstruction or major bleeding.
02Persistent symptoms after a low FITEscalate clinical discordance instead of repeating triage indefinitelyEscalationA 52-year-old has progressive abdominal pain, a 5 kg unintentional weight loss and FIT 4 micrograms/g. Haemoglobin is normal and no mass is palpable, but symptoms persist at four-week review.+
- 1Confirm that the sample was valid and record the numerical result, then reassess weight, abdominal and rectal findings, full blood count, ferritin and inflammatory markers.
- 2Explain that the low value reduces colorectal-cancer probability but does not explain progressive symptoms or exclude a non-bleeding lesion.
- 3Use the local safety-net or specialist advice route to arrange timely structural investigation on the strength of continuing unexplained symptoms; document why further investigation is required.
- 4Verify the diagnostic outcome and provide earlier return triggers for bleeding, vomiting, distension, inability to pass stool or flatus, or rapid deterioration.
03Obstructing colorectal cancerResuscitate and image before any routine referral testA 74-year-old with months of narrowing stool now has marked distension, colicky pain, faeculent vomiting, absolute constipation, pulse 122/min and new kidney injury.+
- 1Begin ABCDE care, keep nil by mouth, obtain large-bore intravenous access and blood count, electrolytes, renal function, lactate, coagulation and group-and-save or crossmatch according to physiology.
- 2Give balanced intravenous crystalloid with repeated assessment, provide analgesia and use nasogastric decompression for persistent vomiting; monitor urine output.
- 3Obtain urgent contrast CT to define tumour level, caecal dilatation, ischaemia, perforation and metastatic disease while colorectal surgery and anaesthesia review the patient.
- 4Agree decompression, stenting, diversion or resection from site, perforation risk, stage and fitness; verify tissue diagnosis and completion staging after immediate source control.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Large-bowel obstruction
A stenosing lesion produces proximal dilatation, fluid and electrolyte disturbance, bacterial translocation and eventual caecal ischaemia or perforation if decompression is delayed.
Perforation and peritoneal sepsis
Tumour necrosis or pressure injury above an obstruction can spill faecal contents into the peritoneum, causing sepsis that requires resuscitation and urgent source control.
Metastatic spread
Portal drainage favours hepatic deposits; lymphatic, peritoneal and pulmonary spread may produce nodal disease, ascites, respiratory symptoms or systemic decline.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track FIT and referral completion rather than assuming the electronic request produced an appointment.
- Review haemoglobin and iron replacement while diagnostic investigation proceeds in parallel.
- Confirm the anatomical extent of colonoscopy or CT colonography and obtain every relevant pathology result.
- After diagnosis, ensure staging and colorectal multidisciplinary-team decisions are communicated to the patient and primary care.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Laterality is a tendency
Right-sided anaemia and left-sided obstruction are useful patterns, but any colorectal location can bleed, obstruct or alter bowel habit.
FIT changes probability
A quantitative result supports triage but neither localises disease nor cancels a palpable mass or persistent discordant symptoms.
Benign disease may coexist
Haemorrhoids or diverticulosis can be present alongside a tumour and must not explain unsupported alarm features automatically.
Emergency presentation alters sequence
Physiological stabilisation and surgical planning precede elective pathway tests when cancer causes perforation, obstruction or major haemorrhage.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling bright-red blood benign without assessing age, bowel habit, weight and iron status can delay rectal or colonic cancer diagnosis.
- 02
Using serum CEA to diagnose a symptomatic patient misapplies a marker used in established cancer management.
- 03
Closing the episode after a low FIT despite a rectal mass or persistent unexplained symptoms creates false reassurance.
- 04
Failing to check examination quality and biopsy results leaves the referral process incomplete.