Firstly, it’s important to note that this isn’t a study in people – this is a study in mice. But these are mice with intact immune systems and they are bearing mouse tumours. It means that although this is an animal model we can trust the evidence a bit more than we can when dealing with immune deficient mice implanted with human tumours. Secondly we should note that these mice were not forced to do exercise – so there was no additional stress involved and there were no enforced amounts of exercise that had to be performed. Basically the mice were given an environment which gave them an exercise wheel they could use, whereas the comparison group didn’t have the opportunity to exercise. Finally, some of the mice had ER+ and some ER- tumours, matching human tumours in hormone responsive and non-responsive sub-types.
What the study showed was that the mice doing the exercise had a reduced the tumour growth rate, an increased the rate of cancer cell death (apoptosis), increased the maturity of the tumour blood vessels, increased tumour blood flow and reduced the areas that were starved of oxygen (hypoxia). These are all things which are positive and which we definitely would want to achieve clinically. Basically these results show that exercise normalises the tumour blood supply. This is a good thing.
Normally the tumour blood supply is chaotic – vessels are immature, leaky, misconnected. This chaotic blood supply has a number of downsides. Firstly it means that the drugs we give cancer patients to kill the tumour often don’t make it into the interior of the tumour – not good because if they don’t in they won’t work. Secondly the chaos causes areas of the tumour to become starved of oxygen and nutrients – this in turn causes the cancer cells to become more aggressive and dangerous as they adapt to these harsh conditions.
So, normalising the blood supply means that tumours are not forced to become more aggressive and, as we see in these results, this can lead to a slower growth rate. It also means that when drugs are administered they can make it into a greater portion of the tumour. And this is where the second lot of results come in. Mice treated with the chemotherapy drug cyclophosphamide had greater response if they were exercising compared to the sedentary mice. Interestingly, mice who did exercise alone (no chemo) showed a similar response to mice treated with chemo alone. But the best response came from mice who had chemo and did exercise.
These are positive results but we do have to keep in mind that this is in mice. However, it backs up what we know from evidence in humans and suggests reasons for why we’ve seen these results. The take home from this is that exercise has a positive effect in breast cancer – and most likely in other cancers too. It doesn’t have to be running a marathon every week either – a study in women with breast cancer back in 2005 found that walking at an average pace for 3 – 5 hours per week had positive effects on survival.