To Screen-or Not?
Questions to put to your physician before having a test
3. What's the likelihood the test will miss the cancer or say I have it if I don't?
No screening test is perfect. Even mammography and colonoscopy can occasionally miss a cancer. Ask about the chance of such a false negative. Tests also exhibit false positives-identifying a nonexistent cancer. Usually a false positive is merely an annoyance, but not always. It ups the ante, often leading to follow-up tests to determine whether that suspicious spot on the film or screen is cancerous or benign or nothing at all. No man wants to go through an unnecessary prostate biopsy because of a worrisome PSA test. Certain follow-up tests, such as open lung biopsy, carry a small possibility of complications. And some tests have a high rate of false positives-about 11 percent of mammograms, for example.
How would you handle a false alarm? Would it keep you up at night for months or roll off your back? If this is an annual test, are you comfortable with the possibility of many false alarms over your lifetime? Again: Ask your doctor to put the risk in meaningful terms, such as the number of false positives per 1,000 people taking the test compared with the number of real cancers that will be found.
4. What other risks does the test pose?
The biggest is overdiagnosis-finding real cancers that don't need treating because they'll never amount to anything. That is especially common for melanoma as well as cancers of the prostate, breast, and thyroid, says Welch. "Even within a given cancer, they're not all the same," says Harris. "Some cancers grow really fast and they're bad, and others just sort of sit there and don't do very much." If screening reveals any cancer, there is considerable pressure to treat it. That is hardly pleasant and has risks of its own; chemotherapy, for example, can damage the heart. And picking up possibly harmless, slow-growing tumors is no guarantee of finding dangerous ones that grow quickly and might slip by between screenings.
For any test, the scope of overdiagnosis isn't always known. Some cases of ductal carcinoma in situ-cancerous cells confined to the milk ducts-progress to invasive cancer; others don't. It's the same for prostate cancer. Worse, medicine can't yet reliably predict whether a particular tumor will be dangerous. "We can't question a polyp and ask its intentions," says Robert Smith, director of cancer screening with the American Cancer Society. Given that uncertainty, it may be hard to calculate whether treating a potentially deadly cancer early will outweigh treating people who didn't need it. But knowing whether research suggests overdiagnosis may play a factor in your decision to have a test.
5. What will happen if the results are positive?
It could mean anything from a repeat test in a few months to a biopsy to more invasive surgery. "If you don't want to take the next step, why do the test?" asks Welch. Don't assume you'll figure out what to do when the time comes.
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