Colorectal cancer

28th June 2014 by NASGP

Colorectal cancer

Aimee Lettis from the GP Update team gives us short, sharp nuggets of clinical information for sessional GPs.

Diagnosing colorectal cancer can be hugely challenging. Many patients come worried they have colorectal cancer and it can be difficult to determine who needs investigation. Focusing on colorectal cancer, survival is significantly better if detected early, but using 2WW guidelines alone will identify only 25% of cases. So what can we do? Well, an interesting article in the BMJ looked at why colorectal cancer is easily missed (BMJ 2013;346:f3172). Before we look at this, here’s a reminder of the 2WW criteria (NICE 2005 CG27):

Change in bowel habit and/or rectal bleeding

  • Age ≥40y with rectal bleeding AND change in bowel habit to looser stools/increased frequency for ≥6w.
  • Age ≥60y with rectal bleeding without anal symptoms OR change in bowel habit towards looser stools/increased frequency for ≥6w.


  • Patients of any age with a right iliac fossa (thought to be large bowel) or rectal mass.

Iron deficiency anaemia

  • Men of any age with unexplained iron deficiency anaemia AND Hb <110g/L.
  • Non-menstruating women with unexplained iron deficiency anaemia AND Hb <100g/L.

Why is colorectal cancer easily missed? BMJ 2013;346:f3172

Worryingly, 50% with colorectal cancer do not meet 2WW criteria at presentation. Audits suggest three groups of symptoms that are common presenting symptoms of colorectal cancer but where early diagnosis is missed because symptoms do not meet 2WW guidelines. These are:

Mild anaemia

  • Consider investigating earlier using higher cut-offs of ≤120g/L in men and ≤110g/L in women >60y (these patients have about a 4% risk of colorectal cancer).

Abdominal pain

  • The most typical symptom of colorectal cancer along with rectal bleeding, but is missing from referral guidelines because of its low predictive value of 1.1% (although this increases to 3% if reported twice).
  • Therefore, be wary of diagnosing IBS in patients >50y without considering other possibilities, e.g. colorectal/ovarian cancer, and whether colonoscopy is necessary before making the diagnosis.

Change in bowel habit

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