What are the symptoms of colorectal cancer?

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When a colorectal cancer first develops and is small it usually causes no symptoms. As it grows, the symptoms that develop can vary, depending on the site of the tumour.

The most common symptoms to first develop are:

Bleeding from the tumour. You may see blood mixed up with your faeces (stools or motions). Sometimes the blood can make the faeces turn a very dark colour. The bleeding is not usually severe and in many cases the bleeding is not noticed as it is just a small 'trickle' which is mixed with the faeces. However, small amounts of bleeding that occur regularly can lead to anaemia which can make you tired and pale.
Passing mucus with the faeces.
A change from your usual 'bowel habit'. This means you may pass faeces more or less often than usual causing bouts of of diarrhoea or constipation.
A feeling of not fully emptying the rectum after passing faeces.
Abdominal pains.

As the tumour grows in the colon or rectum, symptoms may become worse and can include:

The same symptoms as above, but more severe.
You may feel generally unwell, tired or lose weight.
If the cancer becomes very large, it can cause a blockage (obstruction) of the colon. This causes severe abdominal pain and other symptoms such as vomiting.
Sometimes the cancer makes a hole in the wall of the colon or rectum (perforation). If this occurs the faeces can leak into the abdomen. This causes severe pain.

If the cancer spreads to other parts of the body, various other symptoms can develop. The symptoms depend on where it has spread to.

All the above symptoms can be due to other conditions, so tests are needed to confirm colorectal cancer.