World Oncology Forum 2015
Obesity provides a fertile ground for cancer to grow
Dr Michael Pollack - McGill University, Montreal, Canada
It’s interesting that in the present world, unlike all of recorded history, we have a large percent of people who are obese or overweight. In the past we always were limited by the amount of food available and obesity was not so common; now with advertising and with less expensive food, really obesity is becoming an epidemic and it’s been found that, tracking that, obesity is associated with more cancer. So if we project to the future, if more and more people are becoming obese we have to worry about more and more cancer so that’s a trend that we want to stop and we also want to understand the basis of the connection.
Recent research has shown that it’s not just being fat, as it were, that’s dangerous directly. The problem is that if you’re overweight you have changes in the balance of certain hormones and the hormonal environment of an obese person is more conducive for tumours to grow. In other words, if you’re a gardener, an obese person is sort of like having a more fertile soil for cancers to develop. Of course we don’t really mean soil, what we mean in this context is the hormonal environment of an obese person is an environment which cancer cells like. So that’s one reason, one new reason, why we have to fight obesity.
What about data which shows that the link between obesity and breast cancer varies between pre and postmenopausal women?
That is a complex particular point but the bottom line is that most breast cancer does occur in older, postmenopausal women and in that group the overweight or obesity worsens the breast cancer outcome. So in that group two things happen: first of all you’re more likely to have a diagnosis of breast cancer and if you do you’re more likely to do badly. So both for cancer prevention and for improving cancer prognosis we would advise postmenopausal women to watch their weight.
What is the role of drugs in prevention?
Ideally we would like to prevent cancer strictly by lifestyle modifications. We would like to encourage exercise, encourage lifestyle factors, get rid of smoking and let that do the whole job. It’s very important to prevent all preventable cancers by whatever means possible so while we work on the lifestyle with the prioritisation we also are very interested in the possibility that some drugs or health, what we call nutraceuticals, might play a role. These, of course, would have to be well known, extremely safe drugs. We would never give for a purpose of prevention anything that was toxic. So the kinds of drugs that are being studied in this context are drugs like aspirin at low doses and drugs like metformin which are very commonly used for the treatment of diabetes. These are huge fields of active research now so we don’t actually have final recommendations that we can give to the public. But we certainly feel that these areas of research deserve high prioritisation. It’s a little bit unusual because since these drugs are so common and are available generic and are inexpensive, the pharmaceutical industry really has little motivation to develop them for possible applications in cancer prevention because there’s so little money to be made. So it’s interesting that the research that some of these existing commonly used drugs may have additional roles in cancer risk reduction is a job that’s being left to the academic community and not to the pharmaceutical industry as would be the case if they were newly discovered drugs.
What about a “tri-pill” comprising aspirin, metformin and statin.
There are individual rationales for each of those drugs. To put them all together in a cocktail is a little bit of a leap but it’s legitimate research. We don’t know if the effects would be additive or if they would be synergistic or if the combination would actually be better than just using the best one. So I think that that’s one way to go but it’s more of an idea that is based on, well, let’s throw everything we have at the problem rather than an idea that was based on some results in the laboratory that specifically suggested that all three drugs should be used at once. Interestingly, there are some serious ideas that some of these approaches may be useful for overall health rather than just for cancer prevention. It’s well known that there has been discussion about aspirin being useful for cardiovascular disease prevention so the idea that it’s useful, perhaps, for cancer prevention really would be very useful. Because, let’s face it, your average person doesn’t want to have to take twelve pills, one for each of their feared diseases. It would be nicer if you had a combined lifestyle and perhaps one or two drugs that would just be overall good for healthy aging. There’s talk in the United States now about using metformin in a clinical trial to evaluate its overall health benefits in aging people, not just for prevention of cancer but also for better metabolic health and better cardiovascular health.
So, overall, if we want to live longer and if we want to live healthier, in the current environment we have to optimise our lifestyle. We have to recognise that we can no longer count on food supply being so limited that obesity is impossible. Rather, we have to recognise that we have so much food that obesity is a big risk and we have to fight that tendency. Then, ongoing research will tell us whether some of these simple drugs, aspirin, metformin, may or, on the other hand, may not have a role.
