Colorectal Cancer and Polyps

Colorectal cancer is one of the most common cancer types seen in the western world. They are adenocarcinomas arising from adenomatous polyps in the colon and rectum, with a majority seen on the left side of the colon. 

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Anatomy of the large intestine

The large intestine is approximately 1.5m in length and stretches from the caecum to the anal canal. Anatomically it can be divided into

  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon
Large bowel
Arterial supply

The colon is supplied by the superior mesenteric artery (SMA) and inferior mesenteric artery (IMA)

  • Ascending colon – ileocolic and right colic arteries branching from the SMA
  • Transverse colon – right colic and middle colic artery branching from the SMA, and the left colic artery branching from the IMA
  • Descending colon – left colic artery branching from the IMA
  • Sigmoid colon – sigmoid arteries branching from the IMA
Venous drainage

Venous drainage is by the superior and inferior mesenteric vein draining into the portal vein transporting venous blood to the liver.

  • Ascending colon – ileocolic and right colic veins -> superior mesenteric vein
  • Transverse colon – middle colic vein -> superior mesenteric vein
  • Descending colon – left colic vein -> inferior mesenteric vein
  • Sigmoid colon – sigmoid veins -> inferior mesenteric vein
Bowel wall
  • Mucosa – columnar epithelium with mucus-secreting goblet cells
  • Submucosa – containing lymphatics
  • Muscularis propria – circular and longitudinal layer
  • Serosa – connective tissue
Bowel wall

Colorectal cancer

  • Adenoma-Carcinoma Sequence
    • Inherited or spontaneous mutation of APC (tumour suppressor gene) – deregulation of β-catenin protein
  • >90% adenocarcinoma originating in epithelial cells
  • Right sided: exophytic – grow outwards from one location
  • Left-sided: circumferential– obstruct
Clinical features

Left-sided tumours

Right-sided tumours

Emergency presentations

Risk factors


  • Genetic syndromes
    • FAP
    • HNPCC (Lynch syndrome)
    • IBD
    • Acromegaly
  • Family history
    • One 1st degree relative with CRC = 3x risk,
    • Two 1st degree relatives with CRC = 10x risk
  • Ethnicity – Ashkenazi Jews (I1307K APC mutation )


  • Diet high in fat and cholesterol – especially from animal sources
  • Obesity – 30% increase if BMI > 30
  • Alcohol – 40% increase if > 4 units/day
  • HPV (anal cancers)
  • Abdominal pain – SOCRATES
  • Bowel habits
    • Establish what is normal for the patient (usually between 3 times per week – 3 times per day)
    • Duration and degree of change in bowel habits
    • Complete vs partial constipation – complete -> no flatus
  • Blood – fresh, mixed with stool, melaena
  • Constitutional symptoms – weight loss, fatigue, night sweats, signs of anaemia
  • PMHx – IBD, diabetes, previous surgery, cardiac/respiratory disease
  • FHx – malignancy, autoimmunity (IBD)
  • SHx – smoking, alcohol, obesity, WHO performance status
  • Inspection – cachexia, signs of anaemia (conjunctival pallor, koilonychia, angular cheilitis), jaundice, masses
  • Abdominal examination – masses, distension, fluid shift, organomegaly, external hernial orifices
  • Full lymph node examination
  • Digital rectal examination
  • ECG
  • Lateral flow/ Rapid Covid PCR
  • Urine pregnancy test
  • Routine: FBC, U&E, LFT, CRP, Mg, bone profile, amylase
  • Surgical bloods: G&S, clotting
  • Tumour markers – baseline CEA (note: not a diagnostic marker but useful in assessing progression)
  • CT +/- contrast in suspected bowel obstruction
  • Colonoscopy for screening and diagnosis
  • CT CAP for staging
  • CT colonography/barium enema/flexi-sig if colonoscopy contraindicated
  • MRI rectum/anal canal – assess relationship with bowel musculature and other pelvic organs
Modified Dukes staging
Treatment options
  • Stage A/B – surgery
  • Stage C – surgery with adjuvant chemotherapy 
  • Stage D – chemotherapy +/- surgery
    • May be more suitable for stenting, palliative diversions or surgical bypass
  • Laparoscopy or laparotomy
  • Primary anastomosis or de-functioning stoma
  • In an emergency, it is safer to perform a proximal stoma than directly attempt anastomosis
Resection of rectal tumours
  • High-lying rectal tumours (>3cm from anus): high or low anterior resection
    • Primary anastomosis
    • De-functioning stoma
    • J-pouch
  • Low-lying rectal tumours: abdominoperineal resection (APER)
    • Resection of sigmoid colon and rectum
    • Resection of anus through perineum
    • End-colostomy
  • Faecal test offered every 2 years from 50 to 74
  • Faecal immunochemical test (FIT) – sensitivity for colon cancer 97%
    • Specific for lower GI bleeding as globin from the upper GI tract is degraded by digestive enzymes
    • No interference from dietary haem, peroxidases or medications

NICE Guidance recommends that patients should be referred for urgent investigation of suspected bowel cancer if:

  • ≥40yrs with unexplained weight loss and abdominal pain
  • ≥50yrs with unexplained rectal bleeding
  • ≥60yrs with iron‑deficiency anaemia or change in bowel habit
  • Positive occult blood screening test

Colorectal polyps

  • Heterogenous growths in bowel lumen
  • Common, but potential for malignant change 
  • Neoplastoc – Adenoma or polpypoid adenocarcinoma
  • Inflammatory – pseudopolyp (UC)
  • Hamartomatous – Peutz-Jegher’s
  • Hyperplastic – benign
Familial adenomatous polyposis
  • 1% of colorectal cancers
  • Autosomal dominant (but 30% are sporadic mutations)
  • Inhibition of APC tumour suppressor gene
  • Hundreds of adenomatous polyps
  • Usually asymptomatic
    • Unexplained rectal bleeding
    • Abdominal pain
    • Diarrhoea
    • cancers start to develop a decade after the appearance of the polyps
  • Almost all develop CRC by age 40
  • Flexi-sig every 1-2 years starting at age 10-12 to document onset
  • Colectomy before the onset of cancer – usually 20s
Hereditary Non-Polyposis Colorectal Cancer (HNPCC)/Lynch Syndrome
  • Autosomal dominant inheritance
  • Lifetime risk of cancer 85%
    • Endometrial / TCC / gastric / ovarian / pancreatic / biliary / haemotological
    • 3 or more relatives with CRC, two generations
  • Mean age of diagnosis of CRC is 45years
  • Colonoscopy screening – every 2 years from age 20-25
  • Colectomy before the onset of cancer – usually 20s
Peutz-jegher’s syndrome 
  • Autosomal dominant
  • Multiple hamartomatous polyps usually involving small intestine (ileum predominantly)
  • Mucocutaneous hyperpigmented macules of the nose, buccal mucosa, axilla, hands, feet and genitalia
  • Risk of
    • Large bowel carcinoma (39% lifetime risk)
    • Small intestine carcinoma (13% lifetime risk)
    • Gastric carcinoma (29% lifetime risk)
    • Extraintestinal malignancies (breast, lung, pancreas)

Written by Dr Freya Bakko (FY2)

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1 thought on “Colorectal Cancer and Polyps”

  1. I came across a procedure called TEMS procedure used for resection of lower rectal tumors and polyps. Quite frequently done in the UK

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