Exercise is well recognized as being a factor which can reduce the risk of cancer by an average of about 30-40%, with some cancers being reduced by up to 70% in some studies. But what is the situation with people who already have cancer? Can exercise help to reduce the risk of recurrence or even death? There are studies which indicate this is the case in breast and colon cancers and possibly others as well.A study reported in the Journal of Clinical Oncology in 2006 showed that the impact of physical activity on established disease was considerable. They looked at patients with Stage III colon cancer, which is colon cancer that had spread to the nodes, and who had surgery to remove the cancer.The researchers compared those who exercised least (less than, say one hour of exercise per week where they got to the point of sweating) to those who did more than 6 hours of mild to moderate exercise.Those who did more than 6 hours of physical activity had about half the risk of recurrence of the cancer or death from any cause over the follow-up period when compared to those who did not undertake regular physical activity. This is substantial.A similarly positive story is shown in a study of women with breast cancer. Women with stage I, II, and III breast cancer were included in the study. These women were followed for 26 years as part of a major health study looking at many factors. The findings were that exercise reduced total deaths, deaths from breast cancer and recurrence from breast cancer by 40-50%.Now bear with me a little bit because we have to talk numbers. These 50% figures are indicating that approximately half the deaths wouldn't occur in non-exercisers. For those with breast cancer this isn't as great a figure as for colon cancer.In breast cancer the 5-year survival rate is 78% - 85% in Australia, depending on where I get my figures from. This means that somewhere between 15% and 22% die before 5 years. If physical activity cuts those figures in half then you might think that some 7% to 11% of those who get breast cancer could live to that 5-year mark. But it isn't that simple - the reduction is actually 50% of the low exercisers not 50% of the whole group. This should however be compared with the 1.5% impact of chemotherapy on the 5-year survival rate. Exercise is five to eight times better for low exercisers than the expensive side-effect causing chemotherapy.In stage III colon cancer the 5-year survival rate is 30% - 60% depending on where I get my figures again. A 50% reduction in the death and recurrence rate is much more dramatic. But again remember that it is a 50% reduction in the low exercise group, so we cannot say we can cut the death rate in half - it might be a 10-20% reduction if a third of people are inactive. But do compare this with the impact of adjuvant chemotherapy, which is about 1-2% improvement on the 5-year survival rate of colon cancer according to the unemotional medical literature.But regardless of how you slice and dice the figures these studies show that in two cancers, at least, exercise has a very positive effect. So to improve your health, just do it.It is important to remember that in order to maximize the positive outcomes any exercise should be enjoyable - not the grit your teeth and get it done despite the pain, but something you want to go back to time and again. Life is too short at any time to spend hours weekly doing exercise in grim gyms or walking round and round a boring block of residential housing. Go find a place and activity you enjoy.Positive experiences can be measured in the immune system, so organize physical activity that is fun to do and you will get a double whammy - the positive impact of exercise and the input of positive emotions that are known to improve your body's immune system.