Colon Cancer / Bowel Cancer
Colon cancer or cancer of the large bowel develops when cells lining the colon acquire the ability to grow in an uncontrolled manner and to invade local structures. They also acquire the ability to spread around the body and grow in other sites such as the liver and lungs. It is the second commonest cause of cancer death in New Zealand for both men and women. The chances of growing colon cancer increase with age and it is uncommon in people under 50.
As with many cancers it is more likely to be cured if caught in its early stages. In most people colon cancer takes a long time to develop (years). The process starts with minor changes to the genetic material in cells lining the colon. This leads to groups of abnormal cells clumped together to form polyps. Over time further genetic changes allows these cells to invade locally and spread around the body and thus become cancer.
Risks
Colon cancer is common in western countries where the population eats a diet relatively high in animal fats and red meat, but low in fibre. It is also more common in sedentary populations. Obesity and smoking both increase you chances of colon cancer. As we improve our general level of health and live much longer the risk of colon cancer increases. There are a number of genetic conditions that predispose to colon cancer such as HNPCC (hereditary non polyposis colon cancer) and FAP (familial adenomatous polyposis) but these only make up a very small percentage of all colon cancer patients. Having a first degree relative with colon cancer also increases your risk.
To improve your chances of not developing bowel cancer eat a balanced diet with plenty of fruit and vegetables. Maintain a good body weight, participate in regular exercise and don’t smoke. If you have family members with bowel cancer you should discuss colonoscopy screening with your GP (see below).
Symptoms
Unfortunately colon cancer is a silent condition that grows unnoticed until it is large enough to cause symptoms. There are a number of symptoms that should be taken seriously:
Change in bowel habit. Any change in bowel habit whether it is increased frequency or alternating diarrhoea and constipation should be mentioned to your doctor. The change to narrow caliber stools or to different consistency stools also should be investigated.
Bleeding and mucus in the stools are commonly seen in cancers especially on the left side of the colon. If the blood is mixed with the bowel motion or contains little clots or is a funny dark colour then this should be mentioned to your doctor. Clear or bloody mucus or jelly like substance mixed in with the bowel motion is another concerning symptom. Bright red painless bleeding that is on the paper or splatters in the pan is more likely to be an anal problem like haemorrhoids but should always be discussed with your doctor.
Unexplained anaemia (low blood count) especially when due to low body iron stores is seen in patients who have occult (invisible) blood loss from the bowels. This should always be investigated.
Pain is an unusual symptom of colon cancer. It is seen when there are complications from the cancer, for example when the cancer blocks off the colon or when the cancer has perforated. These are medical emergencies and need to be sorted out acutely. Sometimes as the cancer narrows the lumen of the colon patients may experience gripey or colicky pain that is relieved by passage of flatus or stool.
Investigation
If colon cancer is suspected then you should undergo some form of imaging of your colon. The two best options these days are colonoscopy or CT colonography. CT colonography is a new technique which uses a CT scanner to examine the colon which has been purged and then distended with air injected transanally. In most cases any abnormalities that are seen still need to be confirmed with colonoscopy. Colonoscopy involves insertion of a flexible telescope into the cleaned colon. It has the advantage of allowing the specialist to remove any polyps, take biopsies of suspicious lesions and to tattoo cancers so the surgeon can find them easily at surgery.
Once a cancer has been diagnosed you should have a CT scan of your chest and abdomen to look for signs of spread. In patients with a cancer in the bottom part of the colon i.e. (the rectum), it is also recommended that you have an MRI scan to look at how far through the wall of the bowel the cancer has spread.
