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.
So what's the solution to screening for these two cancers?
First, there is hope that these and other screening tests will be honed to make them more useful. Researchers are looking for other blood tests that could aid in identifying and classifying both ovarian and prostate cancers and are figuring out other ways to use them to best pinpoint cancers that really need treatment.
In the meantime, we can also use tests we do have smartly. Andriole noted that part of the downside in PSA testing is not so much overdiagnosis but overtreatment. "If we have a very candid conversation with people who have very tiny tumors, maybe we could spare them the side effects" of aggressive treatment, he said. Indeed, another study out this week found that "watchful waiting," or closely monitoring low-risk prostate cancer without treating it, can be safe and helps men avoid unnecessary treatment. It's important to discuss the pros and cons of the PSA test with your doctor when it's offered.
With ovarian cancer, no major public health group recommends screening healthy women who have no symptoms. However, there is a far greater awareness that quickly reporting symptoms to a doctor can lead to finding cancer at earlier, more treatable stages. If you are experiencing new and persistent bloating, pelvic or abdominal pain, difficulty eating or feeling full quickly, or urgent or frequent urination, tell your doctor. Even lacking evidence that the tests help healthy women with no complaints, the blood test and ultrasound may become common practice for symptomatic women to ferret out the cause of their problems.
What about other cancer screening tests?
There are plenty that are endorsed by major public health entities, namely Pap smears for cervical cancer, several forms of screening for colon cancer (such as colonoscopy), and mammograms for breast cancer. Others, like screening for lung cancer using CT scans, are still under study. The important thing is to ask your doctor about the pros and cons of any screening test before you undergo it, much as you would ask about any other test.