Key Facts

Rectal cancer management differs from colon cancer due to anatomical constraints of the pelvis, relationship to sphincter complex, and the role of neoadjuvant therapy. MRI pelvis is essential for treatment planning.

Epidemiology

Rectal cancer accounts for ~30-35% of all colorectal cancers. ~12,000-14,000 new cases annually in UK. Similar age and sex distribution to colon cancer.

Aetiology

Same as colorectal cancer — adenoma-carcinoma sequence, genetic syndromes, modifiable risk factors.

Pathophysiology

• The rectum lacks a serosal covering in the lower third → tumours can directly invade surrounding structures
• Mesorectum: Fatty tissue envelope surrounding the rectum containing lymph nodes and vessels — complete excision (TME) is critical to reduce local recurrence
• CRM (circumferential resection margin): <1mm = involved → high local recurrence risk; neoadjuvant therapy aims to achieve clear CRM

Typical Presentation

• Rectal bleeding (bright red, mixed with stool)
• Change in bowel habit (increased frequency, tenesmus)
• Mucus per rectum
• Sense of incomplete evacuation
• May present with obstruction or rarely perforation

Examination

• PR examination: Can palpate tumours in lower rectum — assess size, position, mobility, distance from anal verge
• Assess sphincter function pre-operatively

Red Flags

• Fixed tumour on PR — locally advanced, may be T4
• Obstructing tumour — may need emergency defunctioning stoma
• Weight loss and hepatomegaly — metastatic disease

Bedside

• PR examination: Distance from anal verge, mobility, size
• Rigid sigmoidoscopy: Confirms distance from anal verge; biopsy

Bloods

• FBC: Anaemia
• LFTs: Liver metastases
• CEA: Baseline

Imaging

• MRI pelvis: Essential for local staging
  • T stage: Depth of invasion
  • N stage: Mesorectal lymph nodes
  • CRM: Distance from mesorectal fascia (involved if <1mm)
  • EMVI (extramural vascular invasion): Poor prognostic factor
• CT chest/abdomen/pelvis: Distant staging (liver, lung)
• Colonoscopy: Full colonic assessment (synchronous tumours in ~3-5%)
• EUS (endorectal ultrasound): For early (T1/T2) tumours — assesses depth of invasion

Early Rectal Cancer (T1)

• Transanal endoscopic microsurgery (TEMS): Local excision for early, favourable T1 tumours (well-differentiated, no lymphovascular invasion, <3cm)
• If adverse histological features → completion TME surgery

Locally Advanced (T3/T4 or N+)

• Neoadjuvant chemoradiotherapy: Long-course 5-FU + radiotherapy (45-50.4 Gy over 5 weeks) → surgery at 6-10 weeks
• OR short-course radiotherapy (25 Gy in 5 fractions) → immediate surgery (if CRM clear on MRI)
• TME surgery: After neoadjuvant therapy

Surgery

• Anterior resection (AR): Upper/mid rectum; primary anastomosis ± defunctioning loop ileostomy
• Low anterior resection: Low rectum (preserving sphincter); almost always needs defunctioning ileostomy
• Abdominoperineal excision of rectum (APER): Very low tumours involving sphincter complex → permanent end colostomy
• Hartmann's: Emergency presentation with obstruction/perforation

Adjuvant

• Adjuvant chemotherapy (capecitabine/FOLFOX): If node-positive and no neoadjuvant chemoRT given
• Post-operative MRI/CT surveillance

Watch and Wait

• Emerging approach for patients with complete clinical response to chemoradiotherapy
• Regular surveillance (MRI, endoscopy, CEA)
• ~15-30% regrowth rate; salvage surgery usually feasible

Referral Criteria

• All rectal cancers — MDT discussion
• MRI staging before treatment decision
• Specialist colorectal surgeon for TME

• 5-year survival: Similar to colon cancer by stage
• Local recurrence: <5% with TME (vs ~30% historically without TME)
• Neoadjuvant chemoRT: Reduces local recurrence by ~50% in locally advanced disease
• LARS: Affects ~50-70% of patients after anterior resection — frequency, urgency, incontinence, clustering; may improve over 1-2 years
• Permanent stoma: ~10-20% of rectal cancer patients (APER or non-reversal of defunctioning stoma)
• Anastomotic leak: ~5-10% after anterior resection (reason for defunctioning ileostomy)

Rectal Cancer Surgery Decision

Key Trials