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.Â
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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
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
Colorectal cancer
Pathophysiology
- 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
- Early obstruction
- Fresh rectal bleeding
- Mucous discharge
- Tenesmus
- Constipation
- Colicky lower abdominal pain
- Abdominal mass
Right-sided tumours
Emergency presentations
- Malignant bowel obstruction
- Perforation
- Haemorrhage
Risk factors
Inherited
- 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 )
Modifiable
- 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)
Assessment
History
- 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
Examination
- 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
Investigations
Bedside
- ECG
- Lateral flow/ Rapid Covid PCR
- Urine pregnancy test
Bloods
- 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)
Imaging
- 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
Management
Classification
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
Surgery
- 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
Screening
- 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
Types
- 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)
1 thought on “Colorectal Cancer and Polyps”
I came across a procedure called TEMS procedure used for resection of lower rectal tumors and polyps. Quite frequently done in the UK