When a colon cancer is removed the tumour and the surrounding tissues are examined by a pathologist. The pathologist determines the extent, or stage, of the cancer. This is classified according to a system developed by a doctor whose surname was Cuthbert Dukes.

The Dukes staging system is described as follows -

• Dukes A - the cancer is confined to the colon wall
• Dukes B - the cancer has spread through the muscle of the bowel wall, but the lymph nodes aren’t affected
• Dukes C - the cancer has spread to one or more of the lymph nodes nearby.

The staging system gives doctors a guide to the risk of the cancer coming back or spreading to other parts of the body. With Dukes' A tumours the risk is very small, with Dukes' B the risk is increased and with Dukes' C it is further increased.

So the fact that your wife's cancer was a Dukes B indicates that there was some spread of the growth through the wall of the bowel. This means there may be a risk that microscopic cancer cells could have been left behind after surgery or that possibly some cells might have spread to other parts of the body that could later grow into secondary cancers (metastases) elsewhere.
Many people who have Dukes' B cancers of the colon are cured by surgery alone, but unfortunately some are not and go on to develop further problems.

Several clinical trials have shown that if chemotherapy is given to people who have Dukes' B cancers, this may reduce the risk of the cancer coming back and might increase the cure rate. But current figures suggest the number of people who might benefit is very small. It is thought that the people with Dukes B colon cancer who are more likely to benefit from chemotherapy are the following:

• people with tumours whose cells look very abnormal under the microscope (called poorly differentiated tumours);
• people whose tumours show evidence of having invaded the bloodstream (called vascular invasion);
• people whose tumours have obstructed the bowel 
  

The chemotherapy itself often involves treatment for some months and there are normally side-effects. These side-effects vary in severity depending on the exact treatment that is given.They may be quite mild or may be quite troublesome.

Because the results from the studies done so far suggest that only a small minority of patients will actually get a benefit from chemotherapy and because the treatment does cause side-effects, it would be a good idea to discuss with the consultant what the risk is of your wife’s cancer recurring, and what the likely benefits are of her having chemotherapy.