The recent news linking prostate cancer to a virus, XMLV, supports the hope that cancer vaccines will be able to significantly reduce future mortality from the disease. This is crucial if the recent increases in life expectancy are to continue.
Since the 1970s, mortality rates have fallen at an increasing rate. Looking at causes of death, it is clear that the main reason for this is the reduction in heart disease. This used to account for more than twice the number of deaths than cancer. However, the modest reductions in mortality rates from cancer mean that it now kills more people than heart disease. This limits the scope for future improvements in life expectancy, as there is a limit to future falls in death from heart disease.
There have been advances in cancer treatments, but these have been modest. Many of the treatments extend the lifespan of cancer sufferers, but the illness being treated is still the eventual cause of death. The complex causes of cancers – and it must be remembered that there are many different forms of this disease – mean that treatment is difficult, expensive and often harmful in itself.
One of the main reasons for the fall in mortality from heart disease is the reduction in smoking since the 1970s. This has also helped reduce mortality from cancer, although not dramatically. This is despite the fact that smoking is the main cause of many different cancers, and the main cause of cancers in aggregate. The reason for this is that giving up smoking reduces the risk of dying from heart disease very quickly, in a matter of months; however, the risk of dying from cancer remains high for many years. In other words, the fall in smoking has led to a rise in the proportion of surviving, cancer-prone ex-smokers in the population. As, over time, these are replaced by lifetime non-smokers, cancer rates will fall – and then the focus will shift to other causes.
After smoking, the main cause of cancers is thought to be viruses. As with smoking, this gives the opportunity to prevent cancer, rather than try to treat it, and prevention is better than cure. The fact that nearly all cases of cervical cancer are caused by the human papillomavirus (HPV) has led to a vaccine being offered to all teenage girls in the UK over the next few years. This will offer protection from strains of HPV that cause 70% of cervical cancer cases.
Rates of mortality from prostate cancer far exceed those from cervical cancer, so a vaccine preventing even a proportion of deaths from this disease would be a significant breakthrough. The researchers who found the link between the xenotropic murine leukemia virus-related virus (XMLV) and prostate cancer identified the presence of the virus in 27% of prostate tumours analysed, and were able to link the virus to more aggressive incidences of the disease. If a vaccine were to be produced that caused rates of mortality from prostate cancer to fall by a quarter, then perhaps current improvement in life expectancy could continue into the future. This does assume that increasing rates of obesity will not push mortality rates in the other direction – but that is a topic for another post…
