Colorectal cancer

Overview

Colorectal cancer (CRC) is the third most common cancer and second most common cause of cancer death in the UK (~42,000/year). The vast majority are adenocarcinomas arising via the adenoma-carcinoma sequence over 10-15 years.

Risk Factors

Age >50 (90% of cases)
First-degree relative with CRC
Lynch syndrome / FAP
Long-standing IBD (extensive colitis >8-10 years)
High red/processed meat, low fibre diet
Obesity, physical inactivity, smoking

Presentation

Site determines presentation - right-sided tumours are wider calibre and present late; left-sided tumours obstruct earlier.

Right-sided vs left-sided CRC
FeatureRight-sidedLeft-sided/Rectal
Typical symptomIron deficiency anaemia, fatigue (occult bleeding)Rectal bleeding, change in bowel habit, obstruction
Bowel habitOften unchangedLooser/more frequent or alternating
MassPalpable RIF massRectal mass on PR
MetastasesLiver (portal drainage)Liver + lung (lower rectum drains systemically)

Feature	Right-sided	Left-sided/Rectal
Typical symptom	Iron deficiency anaemia, fatigue (occult bleeding)	Rectal bleeding, change in bowel habit, obstruction
Bowel habit	Often unchanged	Looser/more frequent or alternating
Mass	Palpable RIF mass	Rectal mass on PR
Metastases	Liver (portal drainage)	Liver + lung (lower rectum drains systemically)

•Tenesmus - sensation of incomplete evacuation; hallmark of rectal tumours

•Colovesical fistula - pneumaturia, faecaluria, recurrent UTIs (sigmoid/rectal cancer invading bladder)

•Acute presentations - large bowel obstruction, perforation/peritonitis

Investigations

🥇 First-line

•FIT (faecal immunochemical test) - ≥10 micrograms Hb/g triggers colonoscopy referral; FBC for iron deficiency anaemia (low MCV, low ferritin, raised TIBC)

🏆 Gold standard

•colonoscopy with biopsy - visualises entire colon, allows histological confirmation and polypectomy

•Staging (first-line): CT chest/abdomen/pelvis - liver metastases, lung metastases, lymph nodes, peritoneal disease

•Staging (rectal cancer): MRI pelvis - determines circumferential resection margin (CRM), guides neoadjuvant chemoradiotherapy decision

•CEA - not diagnostic; use as pre-operative baseline then 3-6 monthly for 3 years post-resection to detect recurrence

🥈 Second-line

•CT colonography - if colonoscopy incomplete or patient unfit; cannot biopsy

⚠️
CEA lacks sensitivity and specificity for diagnosis - its role is post-operative surveillance only. A rising CEA after resection suggests recurrence.

Management

•Colon cancer Dukes A/B: surgical resection alone (right hemicolectomy, sigmoid colectomy, or anterior resection depending on site) - adjuvant chemotherapy not routinely indicated without high-risk features

•Colon cancer Dukes C: surgical resection + adjuvant FOLFOX (oxaliplatin + leucovorin + 5-fluorouracil) for 6 months - reduces recurrence risk ~25%

•Rectal cancer (locally advanced): neoadjuvant long-course chemoradiotherapy (capecitabine + radiotherapy) then surgical resection; total mesorectal excision (TME) is the surgical standard

•Very low rectal tumours: abdominoperineal resection (APR) - permanent colostomy required

•Emergency obstruction/perforation: Hartmann's procedure - sigmoid resection with end colostomy, avoids primary anastomosis in contaminated field

•Obstructing left-sided tumour (elective bridge): endoscopic colonic stenting - allows bowel preparation and single-stage resection

•Metastatic (liver-limited, resectable): surgical resection of liver metastases + perioperative FOLFOX - potentially curative

•Metastatic (unresectable): palliative FOLFOX or FOLFIRI ± bevacizumab (anti-VEGF); cetuximab (anti-EGFR) for RAS wild-type tumours only

💡
TME (total mesorectal excision) is the surgical standard for rectal cancer - removes the entire mesorectal envelope to achieve clear circumferential margins and reduce local recurrence.

Prognosis

•Overall 5-year survival ~55-60% in the UK; stage I >90%, metastatic <10%

•Poor prognostic factors: advanced T/N stage, involved CRM (rectal cancer), perforation at presentation, poor differentiation, lymphovascular invasion, elevated pre-operative CEA

•KRAS/BRAF mutations are predictive (not prognostic) - determine eligibility for cetuximab (anti-EGFR only effective in RAS wild-type tumours)

NICE 2-Week-Wait Referral Criteria (NG12)

•Age ≥40: unexplained rectal bleeding WITH change in bowel habit

•Age ≥50: unexplained rectal bleeding alone, OR change in bowel habit without rectal bleeding

•Age ≥60: iron deficiency anaemia OR change in bowel habit

•Any age: rectal or abdominal mass on examination

•FIT ≥10 micrograms Hb/g faeces on a symptomatic sample

Staging

Dukes staging and prognosis
StageDescription5-year survival
Dukes AConfined to bowel wall mucosa/submucosa>90%
Dukes BThrough bowel wall, no nodal spread~70%
Dukes CRegional lymph node involvement~40%
Dukes DDistant metastases<10%

Stage	Description	5-year survival
Dukes A	Confined to bowel wall mucosa/submucosa	>90%
Dukes B	Through bowel wall, no nodal spread	~70%
Dukes C	Regional lymph node involvement	~40%
Dukes D	Distant metastases	<10%

Screening and Prevention

•NHS Bowel Cancer Screening Programme: FIT every 2 years for adults aged 50-74 in England; result ≥120 micrograms Hb/g triggers colonoscopy

•Lynch syndrome/FAP: earlier and more frequent colonoscopy surveillance; aspirin recommended for chemoprevention in Lynch syndrome

•Long-standing extensive IBD: surveillance colonoscopy with chromoendoscopy from 8-10 years after symptom onset

🎯
Screening FIT threshold (≥120 micrograms Hb/g) differs from the symptomatic/2WW threshold (≥10 micrograms Hb/g) - do not confuse the two.

Follow-Up After Curative Resection

•CT chest/abdomen/pelvis at 12 and 24 months

•CEA 3-6 monthly for 3 years - rising level suggests recurrence

•Colonoscopy at 1 year post-resection, then 3-yearly if clear