gastroenterologist doctors wellington

Colorectal (bowel) cancer – am I at risk?

Symptoms that might indicate bowel cancer

Bowel cancer has received more publicity in recent times because of a pilot bowel cancer screening programme in Waitemata  and commencement of the programme itself in Wairarapa and the Hutt Valley in 2017, with the other regions to start over the next 4 years. Colorectal cancer occurs in approximately 2,800 New Zealanders each year and is the second leading cause of cancer death, mainly because it commonly becomes symptomatic only when relatively advanced. The average New Zealander’s lifetime risk of this cancer is approximately 1 in 16, but in some people that risk may be significantly increased, particularly in those who have a strong family history of colorectal cancer where a faulty gene may be the cause. There are no other very good predictors of risk so it is important to be aware of symptoms or signs that might need investigation. The average age of diagnosis of colorectal cancer is 70 years, and the risk mainly goes up after the age of 50, but this cancer can rarely occur in people as young as 20 so suggestive symptoms should not be ignored at any age - the rate of bowel cancer in those under 50 has increased threefold in the past 30 years.

Change in bowel habit

A "change in bowel habit" means a change in how often you need to move your bowels, how difficult it is to do so, or a change in the form of the stool e.g. more liquid/looser.  A change in bowel habit is very common occurrence and most of the time it means nothing of concern – a change in your diet, stress, reaction to recent infection, new medications, a change in physical activity, or even just age can cause changes in your bowel routine. A change in bowel habit where symptoms come and go and return to normal in between bouts can be safely assumed to be of no concern.

A change in bowel habit that might mean something more important is when the change is there all the time (persistent) or continues to get worse (progressive). If there is also bleeding from the bowel, weight loss, or continuous abdominal pain in a localized area, then you see your doctor promptly. A change towards looser or more frequent motions is generally considered to be more likely to mean something significant than constipation.


Bleeding from the bowel, when it is red in colour or clots separate from the stool is usually from haemorrhoids (‘piles’), which are large veins in and around the anus. Bleeding from haemorrhoids is typically seen on the toilet paper or even dripping into the toilet, can appear quite dramatic, and will occur at one motion or several consecutive motions but then stops. If such bleeding is very infrequent then it should be of little concern. Bleeding with a lot of pain on passing a stool is usually because of an anal fissure, a split in the lining of the anus commonly caused by passing a very hard stool that should heal over days to a few weeks.

Bleeding that is present frequently or is clearly mixed into the stool needs investigation if you have not had a recent colonoscopy as this may represent a large polyp or even cancer.  Bleeding of blood that is much darker or even black and foul-smelling indicates blood from higher up and this needs to be checked by your doctor.

A feeling of not being able to empty your rectum

This sensation indicates irritation of the rectum which might indicate the presence of a large polyp or cancer in the rectum.  If you have this feeling persistently then you should see your doctor and get checked.

Weight loss

Weight loss can be due to many different reasons but if it is occurring along with a change in your bowel habit or bleeding from the bowel then this might be a sign of bowel cancer, and you should see your doctor promptly.


A slowly bleeding bowel cancer can cause a loss of red blood cells that eventually causes anaemia.  This can cause feelings of tiredness, weakness or sometimes breathlessness.  Iron deficient anaemia can only be identified on blood testing, indicated usually by a low ferritin. It is common in women before menopause occurs, but in men and in both genders after the age of 50 it might indicate slow bleeding from the bowel and should be investigated with colonoscopy +/- gastroscopy.  In women before menopause, if the anaemia is recurrent or associated with bowel symptoms or weight loss then further investigation is probably needed.