Key Facts

Colorectal polyps are abnormal growths projecting from the colonic or rectal mucosa. They are extremely common, found in ~25-30% of screening colonoscopies. While most are benign, adenomatous and sessile serrated polyps are premalignant and their detection and removal is the basis of colorectal cancer prevention.

Epidemiology

Prevalence increases with age: ~25-30% of adults >50 years have adenomatous polyps. Male predominance (1.5:1). Adenomas are found in ~40% of NHS bowel cancer screening colonoscopies. The transition from adenoma to carcinoma takes approximately 10 years in most cases.

Aetiology

• Sporadic adenomas: age, obesity, red/processed meat, smoking, alcohol, physical inactivity
• Hereditary syndromes: FAP (APC gene — AD), attenuated FAP, MUTYH-associated polyposis (AR), Lynch syndrome (MMR genes), Peutz-Jeghers (STK11 — hamartomatous), juvenile polyposis (SMAD4/BMPR1A)
• Protective factors: aspirin/NSAIDs, calcium, folate, physical activity, high-fibre diet

Pathophysiology

Adenoma-carcinoma sequence (chromosomal instability pathway — ~80% of CRC):

• APC loss → β-catenin activation → adenoma initiation
• KRAS activation → adenoma growth
• SMAD4/DCC loss → advanced adenoma
• TP53 loss → carcinoma

Serrated neoplasia pathway (~20% of CRC):

• BRAF mutation → CIMP → MLH1 methylation → MSI-high carcinoma
• Sessile serrated lesions (flat, right colon) are harder to detect endoscopically
• Account for many "interval cancers" (cancers arising between surveillance colonoscopies)

Asymptomatic (Most Common)

• Discovered incidentally at screening or diagnostic colonoscopy
• FIT-positive on bowel cancer screening

Symptomatic

• Rectal bleeding (usually occult; rarely overt)
• Iron deficiency anaemia
• Change in bowel habit (rare unless large/multiple)
• Mucous discharge (villous adenomas — may cause hypokalaemia from secretory diarrhoea)
• Rarely: intussusception (pedunculated polyps), prolapse through anus

Red Flags

• Large polyp with malignant features (hard, fixed, ulcerated)
• Multiple polyps (>10 — consider polyposis syndrome)
• Young patient (<50) with adenomas (hereditary syndrome)
• Polyp with high-grade dysplasia or invasive cancer on histology

Bedside

• DRE: may detect low rectal polyps
• FIT: may be positive (screening or symptomatic investigation)

Bloods

• FBC: iron deficiency anaemia (occult blood loss)
• U&Es: hypokalaemia (rare — secretory villous adenoma)

Imaging

• CT colonography: alternative to colonoscopy; detects polyps >6 mm with >90% sensitivity; polyps found require colonoscopic polypectomy

Special Tests

• Colonoscopy: gold standard — allows visualisation, biopsy, and polypectomy
  • Assess: number, size, morphology (Paris classification: pedunculated Ip, sessile Is, flat IIa/IIb/IIc)
  • Polypectomy: snare removal with diathermy; EMR for sessile polyps >10 mm; ESD for large flat lesions
• Histopathology: type (adenoma, serrated, hyperplastic), grade of dysplasia, completeness of excision, presence of invasive cancer
  • Haggitt classification (pedunculated malignant polyps): levels 1-4 invasion
  • Kikuchi classification (sessile malignant polyps): sm1-sm3 submucosal invasion depth
• Genetic testing: if ≥10 adenomas, or family history suggesting polyposis syndrome; APC, MUTYH, MLH1/MSH2/MSH6/PMS2

Non-pharmacological

• Polypectomy at colonoscopy: curative for most benign polyps
  • Cold snare: preferred for polyps <10 mm
  • Hot snare: for polyps 10-20 mm
  • EMR: piecemeal or en-bloc for sessile polyps >20 mm
  • ESD: en-bloc resection of large flat/early cancerous lesions at specialist centres
• Surveillance colonoscopy (BSG 2020 guideline):
  • Low risk (1-2 adenomas, <10 mm, no HGD): no surveillance or colonoscopy at 10 years
  • Intermediate risk (3-4 small adenomas OR ≥1 adenoma 10-19 mm): colonoscopy at 3 years
  • High risk (≥5 adenomas OR ≥1 adenoma ≥20 mm OR HGD): colonoscopy at 3 years; if high risk again, repeat at 3 years; if clear, extend to 5 years
  • Serrated lesions: SSL ≥10 mm or with dysplasia — surveillance at 3 years

Pharmacological

• Aspirin: chemopreventive evidence (reduces adenoma recurrence and CRC risk); routine use for prevention not currently recommended outside Lynch syndrome
• Celecoxib: reduces polyp burden in FAP but cardiovascular risk limits use

Surgical/Interventional

• Surgical resection: for polyps not amenable to endoscopic removal (size, location, suspicion of invasive cancer)
• Malignant polyp management: if T1 CRC in polyp — assess completeness of excision, invasion depth (sm level), differentiation, LVI; if high-risk features → segmental colectomy
• Prophylactic colectomy: FAP (typically ileal pouch-anal anastomosis at ~20 years of age)

Referral Criteria

• Polyposis syndrome suspected (>10 adenomas) → genetics + specialist centre
• Large complex polyps (>20 mm) → specialist EMR/ESD centre
• Malignant polyp with high-risk features → CRC MDT
• Family history meeting criteria for genetic testing

Most adenomatous polyps are cured by polypectomy. Without removal, ~5-10% of adenomas progress to cancer over ~10 years. Cancer risk increases with polyp size (0.3% for <10 mm, 5% for 10-20 mm, ~15% for >20 mm), villous histology, and high-grade dysplasia. FAP without colectomy has near 100% CRC risk by age 40. Surveillance colonoscopy after polypectomy reduces CRC incidence by ~75-90%. Malignant polyps with favourable features (sm1, well-differentiated, no LVI, complete excision) have <3% lymph node metastasis risk — polypectomy alone may be curative.

BSG Post-Polypectomy Surveillance (2020)

Hereditary Polyposis Syndromes