colorectal cancer 

Written by Aw Pei Ying Amanda Aw

Last Reviewed: September 2019

Review Due: September 2020



‘most commonly adenocarcinomas arising from the glandular epithelial cells of the colon or rectum’



Risk Factors

Increasing age 

Family history (2-3 fold increased risk with one first-degree relative) 



Red meat and processed meat intake


Neoplastic polyps (adenoma-carcinoma sequence) 

Inflammatory Bowel Disease (particularly ulcerative colitis) 

Genetic predisposition/familial syndromes (HNPCC 3-10%, FAP 1%)

Protective Factors

Aspirin > 75 mg/day 

High-fibre diet (reduces intestinal transit time and contact of mucosa with carcinogens)



PR bleeding

Mucous PR 

Change in bowel habits 


PR mass 

Obstruction (20% presenting as an emergency) 

Hepatomegaly/jaundice (if liver metastasis)


Change in bowel habits 


Weight loss

Obstruction (less likely than in right-sided masses) 

Abdominal mass 

Hepatomegaly/jaundice (if liver metastasis)



The adenoma-carcinoma sequence is an accepted model of pathogenesis in sporadic cancers where multiple stepwise genetic alterations accumulate in normal colonic epithelium, resulting in the transformation into adenomatous polyps and finally to an invasive tumour. Examples of implicated mutations include the APC (adenomatous polyposis coli) gene, K-ras and p53 mutations.


Most commonly  tumours (fig.1) arise in the left colon: rectum (38%), sigmoid (21%), descending colon (4%). Thus, only 60-70% of tumours are visible within the range of flexible sigmoidoscopy.

Colorectal Cancer fig1.png

Figure 1

Distribution of colorectal cancer by site 

[Adapted from Bailey & Love’s Short Practice of Surgery]

Colorectal adenocarcinoma commonly spreads by direct invasion of bowel walls, or lymphatic and haematogenous spread to the liver and lungs, which are the most common sites of metastasis.





For evidence of iron-deficiency anaemia


For evidence of liver metastasis


For baseline renal function, which may be deranged in advanced disease that causes ureteric compression

Faecal Immunochemical Test (FIT) 

Can be offered to symptomatic patients

Carcinoembryonic Antigen (CEA)

Not useful as screening test or to make a diagnosis however can be used for monitoring post-treatment or for disease recurrence


Flexible Sigmoidoscopy or Colonoscopy

Gold standard investigation for colorectal cancer.

Allows direct visualisation and biopsy of lesion (although flexible sigmoidoscopy only allows direct visualisation up to the splenic flexure).

Full colonic visualisation by colonoscopy is usually required in suspected colorectal cancer due to 3-5% risk of synchronous polyps or tumours, provided the patient can undergo a rigorous bowel prep regimen.

CT Chest, Abdomen and Pelvis 

For staging and investigating for evidence of metastasis.

Transrectal Endoscopic Ultrasound + MRI Pelvis 

Allows for delineation of tissue plane involvement which is important in rectal cancer.

CT Colonography 

Less invasive than colonoscopy but may still eventually require colonoscopy if a biopsy is required.


Screening is automatically offered every two years to all men and women aged 50–74 years old in Scotland or 60-74 years old in England and Wales (those aged 75 or over are able to request a test every two years).

The faecal immunochemical test (FIT) replaced the guaiac faecal occult blood test (gFOBt) in 2017:

FIT measures micrograms of human haemoglobin per gram of faeces (µgHb/g faeces) while gFOBt only detects the presence or absence of haem in stools.

A screening result of >80 µgHb/g faeces triggers a referral for colonoscopy


Separate screening tests are available for patients with IBD and those with familial cancer risk.



Staging has an important role in estimating prognosis and guiding the management of colorectal cancers. Pathological staging of colorectal cancer is traditionally reported in terms of the Duke’s Classification. However, the TNM staging system is currently the clinical standard.




The aim of surgery is to remove the primary lesion (via colectomy) and its draining regional lymph nodes for accurate staging.


  • Colon Cancers

    • Segmental resection with stoma or restorative anastomosis 

    • Hartmann’s procedure (for emergency bowel obstruction) 

  • Rectal Cancers

    • Total mesorectal excision (TME) with low rectal anastomosis or abdominoperineal excision + permanent colostomy

    • Transanal endoscopic microsurgery (done with proctoscope for localised disease)

  • Metastatic Disease 

    • Liver resection (avoid biopsy of potentially resectable hepatic metastasis due to risk of tumour dissemination)



  • Options for surgical treatment in palliative cancer include diverting colostomy or colonic stent 



  • Useful for rectal cancer but not colon cancers 

  • Neoadjuvant (prior to surgery) radiotherapy for rectal cancer reduces local recurrence rates



  • Adjuvant (following surgery) chemotherapy improves survival in T3 (Duke C) colon cancer 

  • Can also be considered in high-risk T2 colon cancer

Biological Therapies

  • Bevacizumab (anti-VEGF) can be used with combination therapies for advanced cancers 

  • Cetuximab, panitumumab (anti-EGFR) can be used for KRAS wild-type metastatic colorectal cancer



Colorectal cancer is the third most common cancer worldwide and the second most common cause of cancer death in the UK.

In Scotland, it is the third most diagnosed cancer with 95% of cases occurring in people aged over 50 years. The majority of cases are adenocarcinomas.



  1. Stein DE. Colorectal Cancer. BMJ Best Practice.

  2. Bailey & Love’s Short Practice of Surgery. 27th edition.

  3. Oxford Handbook of Clinical Medicine. 9th Edition. (2017). 

  4. NICE. Colorectal Cancer: Diagnosis and Management. 

  5. NHS Health Scotland. Bowel screening for health professionals. (2017)