One vision for the future is that all young adults, say at age 20, would undergo genetic testing to learn about their risk for major diseases such as heart disease, psychiatric disorders, diabetes, and cancer. It's a vision articulated by the head of the Human Genome Project, Francis Collins, who in a report to Congress stated that "a baseline genome scan could give patients and medical service providers helpful information about an individual's disease risk profile and point to which prevention strategies when available should be put into place."27 While I have no doubt that a genome scan could provide such information, I'm a little less sanguine about the "helpful" part. Let me tell you two reasons why.
Genetic tests can't erase the uncertainty of who will get cancer. Doctors didn't need every single child read DNA to know that some cancers have a strong genetic component. It's obvious: there are families in which many members develop the same cancer at a relatively young age. It is for people in these families that genetic tests are arguably the most useful. A positive test means you have the cancer gene, a negative test means you don't. But a positive test doesn't mean you definitely will get cancer, and, more important, a negative test doesn't mean you won't.
Take the most familiar genetic test, for BRCA1, the abnormal gene associated with breast cancer. Consider a 30-year-old female. If she has a positive test, her risk of developing breast cancer by age 70 is around 50 %. (That is simply the chance of being diagnosed with cancer, not the risk of dying from it.) If she has a negative test, her risk of the identical is just a little below average around 10%. That's because most breast cancers like most other cancers are not the result of a single genetic defect.
This information may be helpful to some and not others. Whether it is helpful hinges on how the result affects the course of action: how mammography is used, whether the woman decides to undergo immediate mastectomy, whether she changes how she lives her life. The test is also helpful if the individual tested is certain she will take one strategy facing a probability of 50% and another one facing a probability of 10%.
But if she will do the same thing either way, then I'd argue the test isn't really helpful. Certainly, it might be even more helpful if it better distinguished the probabilities: if positive meant 100 % chance and negative meant no chance. But that isn't the case. The majority of us don't have such a strong family history for cancer. And most of the cancers treated by doctors don't have strong single-gene origins. Instead, most cancers are caused by multiple genetic alterations in an organism being exposed to multiple environmental factors (most of which occur naturally).
And even if we could catalog every possible genetic alteration (which is conceivable) and all the environmental influences at play (a tougher nut to crack), we never can be certain about the role of chance. That's right: some people get cancer due to bad luck. So what can most of us expect from genetic testing? By testing multiple genes, we are better able to estimate an individual's risk of developing certain cancers. Of course, we've been able to provide a crude estimate of risk, based on age, race, and sex, for many years.
Agenome scan will merely further refine this risk. But for the majority of us the risk refinements will probably fall within a fairly narrow range of relatively low probabilities: lowering it from 10 to 5%, or raising it from 2 to 6%. Although some may emphasize that we've been able to inform people that their risk is "cut in half" or "increased threefold," I doubt that will provide a strong enough rationale for a change in behavior.
Genetic tests can't answer the question of what to do next. Imagine you're a 20-year-old female having just undergone a baseline genome scan. Your risk profile shows you possess an 8.% chance of developing ovarian cancer sometime that you experienced. That's four times the risk for an "average" woman. You don't have the aberration strongly associated with an increased risk of lung cancer in both smokers and nonsmokers, meaning your risk for this cancer is well below average.
You then have a DNA variant that some researchers believe increases your risk of breast cancer by almost 50%, although your doctor reassures you that this point has seen considerable debate in the literature recently. Another gene variant is present that substantially increases your risk for a rare form of a salivary gland cancer, but it's so rare that your doctor suggests you be done with it. Otherwise your risk for the other common cancers is about average. Your genome scan also provides information about other diseases.
Your risk of heart disease is 25% higher than normal and your doctor reminds you that you need to take that seriously, since heart disease is by far the major cause of death across the span of life. This finding doesn't really surprise you because your mother had heart disease a couple of years ago. The same aberration that lowers your risk of lung cancer seems to also lower your risk of death from pneumonia or influenza (although this won't be important until you are much older).
Finally, you have a form of a gene that has been seen as to increase the risk of stroke, but lowers the risk of blindness. Researchers are actively working to better quantify this relationship. Now what? Oops, the genome doesn't answer that question. Some might argue that the first step would be to handle the fourfold increase in the chance of ovarian cancer perhaps by removing your ovaries. Others might point out that heart disease is a more likely cause of death for you particularly after age 50.
Taking out the ovaries and thus inducing menopause might only increase your risk. Another person might suggest removing your ovaries and starting estrogen replacement, which might shield against heart disease though someone else would no doubt point out that that will increase your risk of breast cancer.
Issues bigger than medical care arise as well. What if you wish to have children? Perhaps you should start now rather than waiting. But what if you're unmarried and were planning to stay that way not less than another five years? Well, perhaps you should adjust your vision for the future. Then again, maybe you shouldn't.
Perhaps I am guilty of creating a scenario where the choices are too stark. There is, of course, a middle ground: the best thing might be to have regular (say annual) abdominal ultrasounds. But even this approach is not innocuous. As we have seen, ultrasounds can identify many abnormalities on the kidney. And radiologists can't always distinguish between benign ovarian cysts and ovarian cancer. A strategy of annual abdominal ultrasounds beginning in women 20 years of age will lead to frequent biopsies and, occasionally, unnecessary removal of ovaries and kidneys.
To know whether the regular ultrasound strategy helped more than it hurt would require a randomized trial. But that would be very difficult for two reasons. First, it would need to be restricted to a select group of women: those with the gene associated with ovarian cancer. Second, it would need to follow them for many years: from their 20s into their 40s and 50s. And the same sort of research would be needed for each gene abnormality–early detection strategy combination.
But aren't we obligated to make such an effort before we embark on this kind of genetic testing? Otherwise, all we are doing is getting young people to focus prematurely on death (and perhaps distracting them from their highest risk for death soon: accidents). If we really have little idea of what to do differently, this kind of broad-based genetic testing merely adds clutter. Moreover, it further distracts from the concept of medicine: rather than making sick people well, we end up making well people sick.
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