I was invited to talk about prevention of breast cancer in low and middle income countries. Potentially 75% of cancers can be prevented but for breast cancer it is actually largely unpreventable - only 10% of breast cancers can be prevented. This 10% is where you find that there is a genetic mutation such as the BRCA1 or the BRCA2 which can predispose to breast cancer. So in those sorts of cases the only prevention is actually to remove both the breasts. But for the other 90% of breast cancers we actually do not know the cause. We only talk about the risk factors which are responsible for breast cancer and these risk factors are broadly divided into reproductive risk factors. Reproductive risk factors are those associated with oestrogens in your body. For example, if you have early menarche and late menopause there's a prolonged period of exposure to oestrogens and this predisposes you to breast cancer, so the risk is increased if you have early menarche or late menopause, then if you start your periods early or you end your periods later than the usual woman. If you have your first child after the age of 35 it also increases your risk. If you have many children and you breastfeed your children for more than six months it reduces the risk of breast cancer.
The second main broad risk factors are the lifestyle. Now, there's actually no diet that can prevent breast cancer but the incidence of breast cancer varies throughout the world. For example, the lowest incidence is actually found in Asian women and we think that it is because Asians tend to take a lot of soy-based products. But the data on whether soy prevents breast cancer is actually rather controversial because there are studies that show that consumption of large amounts of soy can actually protect you from breast cancer. These are actually population studies because populations that eat a lot of soy actually have a lower risk. The risk is actually highest in the Western world and what lifestyle factors would you think of in the Western world that predispose you to a higher incidence? This would also be, in a way, diet, lifestyle because in the West women are having their children later, they have less children and they don't really breastfeed for long periods. So these are the risk factors that may reduce the risk of breast cancer. Other than that, most breast cancers are largely unpreventable.
The other part of my lecture is the recommendations of what we can do to reduce the risk of breast cancer. We advocate lifestyle changes and in the traditional Asian population we will advise them not to change their diet because there are a lot of dietary changes. The best way would be to have children early but because as a country develops and there is more women's liberation women are given the choice whether they want to have children early. So a lot more women are going out to work, they join an increasingly sedentary lifestyle, they have their children late, they have fewer children. So that could increase the risk of breast cancer. You find that in low and middle income countries the incidence of breast cancer is increasing, mainly because of these changes in lifestyle.
The other thing that I'm going to talk about is secondary prevention. Primary prevention is generally not very successful so secondary prevention means detecting a cancer early so that your mortality is reduced. In low and middle income countries there's no population based screening mammography programme because of the cost and also women may not come for screening. The other issue about screening mammograms is they are generally not very useful in younger women. That's another thing, in low and middle income countries women present at a younger age. The median age of presentation is 50 years old compared to the Western countries, the developed countries, where the average age of presentation is 60 years old. So generally screening mammography may not be so useful.
The other thing, besides the cost, is that there are no huge randomised controlled trials on screening mammography in low and middle income countries so we will not know whether they are going to reduce mortality as it has been shown in the Western world where all the randomised controlled trials on mammography have been done. The other methods of early detection such as breast self-examination and clinical breast examination, the effect is largely unknown because the Shanghai trial on breast self-examination has shown that there has been no decrease in mortality in the group that practice breast self-examination. There is no randomised controlled trial on clinical breast examination that has shown any reduction in mortality rate. There is a randomised controlled trial on screening, clinical breast examination, in India but so far there have been no long-term results that show that there has been a decrease in mortality from breast cancer by clinical breast examination.