If you’ve heard anything about personal genome testing, it’s that such tests can sometimes reveal people are carriers of genetic mutations that increase the risk of certain diseases. There are many examples with more added each year, such as the BRCA1/BRCA2 genes associated with breast and ovarian cancer. If you’re a woman whose genome has tested positive for a mutated BRCA1 gene, the questions are: What does this mean? What can I do about it?
Such questions are launching a new field of medicine: genetic risk intervention (or prophylactic risk reduction). If you’re a woman identified with a mutated BRCA1/2 gene, then studies show that over a lifetime you are 56% – 80% more likely to develop breast cancer than women without the gene. These are not long odds. Many women would prefer (or insist) that something be done. That something could be mastectomy (removal of the breasts) or a salpingo-oophorectomy (removal of the fallopian tubes and ovaries). Both are serious procedures with obvious personal implications. Nevertheless, some women are going to see them as justified against the odds of dying from cancer.
A new study, conducted by the University of Pennsylvania, School of Medicine (USA) and published in the Journal of American Medical Association (JAMA, September 1, 2010) indicates that this sort of intervention, specifically prophylactic surgery, works.
The study, which included 2,482 women with BRCA1 or BRCA2 mutations (determined between 1974 and 2008), was conducted at 22 clinical and research genetics centers in Europe and North America. The women were followed up until the end of 2009.
The researchers found that risk-reducing mastectomy was associated with a decreased risk of breast cancer in BRCA1/2 mutation carriers, with no breast cancer events occurring in women who underwent risk-reducing mastectomy during 3 years of prospective follow-up. “In contrast, 7 percent of women without risk-reducing mastectomy over a similar follow-up period were diagnosed with breast cancer,” the researchers write.
This result is not counter-intuitive, but it is not overwhelming. It’s an indicator that this kind of risk intervention has yet to come out of the margins of medical procedures. There are several important and difficult questions yet to be answered:
How accurate and reliable are the genome tests? They are improving, even as they become less expensive, but genome tests are far from infallible.
How certain are the links between having a mutated gene and developing the related medical problem? This is a difficult question because of the many variables that enter in to the steps between having a mutated gene and its expression in some form of disease or disability. Experiments and surveys show a correlation or even a causal relationship between specific genes and certain diseases, but in most cases the conditions for this linkage – the genetic and biochemical details – are unknown.
How effective are the prophylactic measures? The field of genetic risk reduction is so new that statistics are incomplete, at best. It’s almost certain, however, that no procedures will be 100% effective. The risk of failure will have to be part of the consideration.
What, if any, are the risks of interventions? Some of the intervention approaches, such as surgery, carry their own risks. Complications from removal of (any) organs are not uncommon. Beyond the medical procedures there are almost always social and psychological risks.
How much will intervention cost?
This last question – cost – goes to the heart of a common problem in modern medicine: There are many life-prolonging procedures but many of them are very expensive, far beyond the means of an average person and generally beyond the acceptance of health insurance programs. While obviously a mastectomy to prevent the occurrence of breast cancer is not the same as a ‘boob job’ (voluntary cosmetic surgery), it’s still ‘optional.’ Optional in this context will often mean affordable or not affordable. This kicks genetic risk intervention into the arena of rich versus poor, with all its social and political issues.
At the moment risk intervention is mostly defined by surgery, preventive chemotherapy, and lifestyle changes. In the future, interventions will also be carried out on the genome, pre-birth or as an adult. For now, however, our knowledge about links between various genetic markers, the path of disease development, and the measures that could be taken to prevent a disease is, to put it charitably, in its infancy.
Someday scientists and doctors may know enough about the causes of various genetically related diseases to be able to pin down the risk. But that isn’t today or anytime in the near future. Cancer, for instance, is still undergoing a research revolution as molecular biology seeks to discover the underlying organic chemistry. Those discoveries must include understanding how environment and lifestyle play a role in the expression of genetic potentials. Since there are many kinds of cancer and a world full of personal and environmental variables – an accurate and complete understanding of any one person’s risk is going to be difficult to achieve any time soon.
That won’t stop the development of genetic risk intervention. There will be a demand for the procedures, and there will be a market; but genetic risk intervention will undoubtedly be added to the list of controversial and yes, risky, new medical technologies.