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Colorectal Cancer

3rd most common cancer in the UK.


Patients present with PR Bleeding, Change in bowel habit, Tenesmus, Weight loss, Anaemia, or Obstruction.


Pathophysiology

Chromosomal Instability Pathway (Adenoma-Carcinoma Pathway) - 70% of cases - Normal mucosa → Adenoma → Invasive adenocarcinoma.


Microsatellite Instability Pathway (Serrated Pathway) - 30% of cases - Cancer arises from serrated polyps (have a serrated/saw tooth appearance microscopically).


Risk factors

  • Increasing age

  • Hereditary syndromes - FAP (Familial Adenomatous Polyposis), Lynch syndrome (Hereditary nonpolyposis colorectal cancer/HNPCC)

  • Long-standing IBD (10+ years)

  • Polyp

  • Diet - low fibre, high animal fat/meat/refined carbs


Familial Adenomatous Polyposis (FAP) - Autosomal dominant condition of TSG mutation where pts develop 100s of adenomatous polyps, making them virtually guaranteed to develop colorectal cancer by their 20s. This is managed with a prophylactic panproctocolectomy.

“Cut open section of colectomy specimen showing hundreds of small polyps throughout the entire colon” © Department of Pathology, Calicut Medical College (Licensed under CC-BY 4.0) https://creativecommons.org/licenses/by/4.0/


Lynch Syndrome (Hereditary Non-Polyposis Colorectal Cancer/HNPCC) - Autosomal dominant condition of mismatch repair genes (MLH1/MSH2) that carries a 80% risk of developing colorectal cancer by their 30s. This is managed with regular endoscopic surveillance.


Bowel Cancer Screening Programme

The aim of this is to detect bowel cancer at an early stage, when it's easier to treat. It includes:

  • FIT test every 2 years for patients aged 60-74 yrs

    • If +ve, pt is offered a colonoscopy


Patients should be 2-week referred if:

  • 40+ with unexplained weight loss + abdominal pain

  • 50+ with unexplained rectal bleeding

  • 60+ with IDA or changes in bowel habit

  • Proven faecal occult blood on testing


Investigations

Faecal tests:

  • FOB (Faecal Occult Blood) - This test picks up any type of blood present in stool, therefore will be +ve even if the patient eats red meat.

  • FIT (Faecal Immunochemical Test) - This test only picks up human blood, as well as inflammation. This makes it very sensitive to bowel cancer (if -ve, you can more or less rule it out).


Investigations:

  • Colonoscopy

  • Bloods - FBC, U&E, LFT, CEA

  • MRI for rectal cancer

  • Staging CT


N.B. CEA isn’t diagnostic but can be used to monitor therapeutic response to interventions.


The cancer is classified with Dukes Criteria.

Management

Bowel resection +/- adjuvant chemoradiotherapy

“Diagram showing an abdoperitoneal resection of the bowel” © Cancer Research UK (Licensed under CC-BY 4.0) https://creativecommons.org/licenses/by/4.0/


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