As a preventive medicine expert well versed in the subtleties of screening, I note that this is not news to me. Cancer screening is, in the most literal sense, looking for trouble. That can be a good thing when you are well prepared to deal with the trouble you find, but if not, what you find is, in fact, trouble with that proverbial capital T.
However, the flip side of today's news is equally important: Just because we can't screen for something perfectly, doesn't mean we shouldn't! So where's the sweet spot? Not as hard to find as today's news may make it seem. This crash course in the hows and whys of cancer screening can help. Master these few, simple principles, and you will be in a good position to get the best out of the science, and art, of cancer screening, while avoiding its pitfalls.
1. We screen best for predictable disease. The reason that prostate cancer screening is controversial is not really our inability to find prostate cancer early, but our inability, thus far, to predict what early stage prostate cancer will do. Many early stage prostate cancers, if left alone, just sit there and cause no discernible harm. In such cases, any "cure" is apt to be worse than the disease—and this is part of the reason why there is still no clear net benefit of routine prostate cancer screening. Today's Times piece simply notes that this is sometimes true of breast cancer as well, although to a lesser extent. So the take away for you is this: When considering a given screening test, ask your doctor if it will be clear what to do if the test is positive for an early stage cancer? Can you predict the behavior of the cancer, and thus the benefits of treatment, with confidence—or not?
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2. It’s about YOU. The likelihood that you have a cancer that will be found through screening and treated to your benefit is uniquely about YOU. It depends partly, for example, on your family history, your lifestyle, your particular genetics. If your family is prone to aggressive breast or prostate cancer, the likelihood rises that you may be, too. And thus, the higher your personal risk of the disease, the greater your likely personal benefit of screening. We will get better at predicting personal cancer risk and screening benefit when genomic assessment reaches its full potential. For now, here's your take away: ask your doctor how your cancer risk compares to the average, and whether screening is more, or less, likely than in the average case to work in your favor.
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3) It's about the test. Medical tests are routinely characterized in terms of sensitivity and specificity. A sensitive test will reliably find a disease when it's there, but at the risk of suggesting it's there when it isn't (called a false positive). A specific test will reliably indicate the disease is not there when indeed it isn't, but at the risk of saying it's not there when it is (called a false negative). Often, the more sensitive the test, the less specific and vice versa, although the occasional and truly excellent test—colonoscopy is a good example—is both sensitive and specific.
These statistical constraints generally mean that a test useful for finding a cancer reliably will issue false alarms pretty often. This is particularly true of mammography, where approximately 12 out of 13 “abnormal” mammograms may prove to be such false alarms. To derive a benefit from screening in such cases, you need to be ready for the anxiety that may come of an abnormal test that proves to be a tempest in a teapot. Your take away here is this: Ask your doctor about the sensitivity and specificity of the test, and how you are prepared to deal with the possibility of a false negative, or more commonly, false positive result. Forewarned is forearmed, and a plan beats a surprised reaction every time. Some medical centers have comprehensive breast care facilities, where a questionable mammogram can be immediately followed up with more specific, definitive tests, so you are not left to toss and turn your way through a sequence of sleepless nights waiting to find out if you are a false positive in the majority, or a true cancer in the minority.
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4) Perfect is the enemy of good. There is no perfect screening test, so don't expect one. The reason to screen for cancer is not because of guaranteed benefit with zero risk; it's because the probability of benefit is greater than any risk or potential harm. So go in knowing a cancer can be missed; an abnormal result may be wrong; and if an early cancer is found, it may not be entirely clear how best to treat it. The take away here: be realistic. Even at its life-saving best, medicine is never perfect, but that life-saving best is pretty good!
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5) Ask an impartial referee. What is most surprising about today's story is that it comes from leadership at the American Cancer Society. After all, if there weren't something productive to do about cancer, the ACS would have little reason to exist. So the Society has tended to be in the vanguard of those recommending screenings. Also in that vanguard have been the specialty societies that do the particular testing in question—urologists, for example, tend to be more enthusiastic about prostate cancer screening than doctors overall; gynecologists may be most tempted to recommend screening for ovarian cancer; and so on. Fortunately, there is a place to go for an objective, evidence-based opinion that is not housed in any specialty. A multidisciplinary group of experts called the United States Preventive Services Task Force issues just such opinions, and they are accessible to you—and your doctor. So your takeaway is simply this: Ask your doctor, or find out for yourself, what the US Preventive Services Task Force has to say about any screening test you are considering.
As for a bottom line on today's controversy: I consider the evidence convincing that overall, breast cancer screening saves lives. There is evidence of net benefit from mammography despite its undeniable limitations, and I recommend it enthusiastically. I find the evidence for prostate cancer screening inconclusive, and don't think we can do better than encourage dialogue about it between doctor and patient with individualized decisions. In this, as in all things (more or less), I practice what I preach: my wife is routinely screened for breast cancer, while I have thus far opted out of prostate cancer screening. We will both be due for colon cancer screening before too long, and will both certainly get tested.
One final point. At its VERY best, cancer screening finds cancer early—and makes a cure possible. But even that is not as good as never getting cancer in the first place! The evidence is very strong that by not smoking, being physically active, eating well (you know what that means!), and controlling your weight, you can reduce your overall risk of cancer by at least 30%, possibly as much as 60%. One of the reasons I feel comfortable opting out of prostate cancer screening is that I know I am doing all I can to minimize my risk of developing prostate cancer in the first place. No matter what modern medical testing comes up with, there will be no substitute for taking good care of yourself. And there's no controversy about it, either.
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