Cancer screening is in the news again. Researchers said last week that they had some potentially encouraging news about methods for screening for ovarian cancer, though it is far too early to endorse their use. Now, in the New England Journal of Medicine, two teams of researchers are reporting preliminary—and apparently conflicting—results from ongoing trials studying how well screening for prostate cancer works. One study found a potential benefit; the other, none. It makes for confusing headlines, and consumers might be left wondering: What am I to do? Here's a primer to help you make sense of the evidence.
To start with the most recent news: What's going on with screening using the prostate specific antigen test?
It may surprise you to know that while most men over 50 have had a PSA test, there is currently no solid evidence that doing so can save lives. There has been much anticipation about the results of two large trials studying this question, and this week we got some early reports. (Both trials will continue for several years with the aim of producing final conclusions.) One study, done in the United States, found no reduction in mortality over about 11 years from a screening program that uses the PSA test and a digital rectal exam; the other, in Europe, using just the PSA test, found a 20 percent relative drop in the death rate from prostate cancer after nine years. That translated to about 7 fewer deaths from prostate cancer for every 10,000 men screened.
The take-away: well, not much. Most public health groups still recommend the PSA at least be offered to men over 50, with an accompanying explanation of its risks and benefits. Men with a life expectancy of less than seven to 10 years probably don't need to undergo PSA testing, Gerald Andriole, a urologic surgeon at the Washington University School of Medicine in St. Louis, said during a conference call about the U.S. study, of which he is an author . . . but we kind of knew that already.
But finding prostate cancer early must be good, right?
Not necessarily. Finding and diagnosing any cancer early is helpful only if it actually affects the course of the disease—that is, if finding it early means you can save lives, says Robert Smith, director of cancer screening for the American Cancer Society. It's possible, however, for screening to catch slow-growing cancers that would never be lethal and yet miss aggressive tumors that spring up and spread in between screenings. In fact, there's pretty broad agreement that doctors treat some men for prostate tumors that never would have caused them problems, but it's not clear how many.
It's also unclear how to pinpoint which newly diagnosed cancers are potential killers and which are, as Andriole called them, "toothless lions." It's an important question to answer, not in the least because the potential side effects of prostate cancer treatment, including impotence and incontinence, are life-altering. It's even possible that treatment itself could shorten a patient's life by causing radiation damage or other delayed effects.
What about ovarian cancer screening? Wouldn't it be best to find that disease ASAP?
Everyone certainly hopes so. There's no current recommended screening regimen for the disease, but researchers are looking at some combination of a blood test called CA125, now used to track the progress of existing ovarian cancers, and a transvaginal ultrasound to visualize any tumors. This screening would be for postmenopausal women. As reported last week in Lancet Oncology, those tests may be promising. But again, while we know that cancers caught early tend to be more treatable, it's not clear that a screening program will help women live longer.
If we're not sure, isn't it safer to just tell all women to get a CA125 blood test?
No, says Ernest Hawk, vice president and division head of cancer prevention and population sciences at M. D. Anderson Cancer Center in Houston. First, we don't know if the test actually works to save lives, so it's not yet clear there's a benefit. And there is plenty of evidence that it could harm women. Following up on suspicious findings would result in many unnecessary surgeries, which carry their own risks. As with prostate cancer, we might end up treating cancers that never would have amounted to anything if left alone, Hawk says.