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In the pipeline: Advances in cancer screening
Beyond cancer: 3 other ways you could be overtreated
Ask Shannon Brownlee your questions about cancer screening tests
Suzanne Bull always half expected that she'd get cancer. After all, she lived in Marin County, California, where breast cancer rates are among the highest in the country. Still, she was determined to do whatever she could to protect herself. She ate right and exercised, and every year, she went into San Francisco to get a mammogram.
Last year, when Bull was 54, she got the news she'd been dreading. An ultrasensitive digital mammogram showed a suspicious spot on her left breast. A biopsy confirmed it was cancer. Fortunately, the surgeon told her, it had been caught early: She had ductal carcinoma in situ, or DCIS, which meant that the cancer was still confined to a single milk duct. And it might well stay there, he added, since DCIS generally doesn't become invasive. That all sounded great, Bull recalls, until the surgeon told her that there was no way to know whether her cancer would turn out to be the lazy, nonthreatening type of DCIS or the potentially invasive kind. She needed a lumpectomy, he told her, and should also consider undergoing radiation and taking the drug tamoxifen.
Bull agonized over the decision for two weeks but in the end went ahead with the lumpectomy and radiation. "I had to do everything I could to stop this disease," she says. With two clean mammograms behind her, Bull feels lucky. "I'm just glad I had access to digital mammography," she says. "It finds things so much earlier."
It's hard to believe, but some researchers wouldn't call Bull lucky at all. They say that yearly mammograms are not nearly as effective at reducing the risk of dying of breast cancer as most women think, and that mammography leads many women to get unnecessary treatment -- especially those diagnosed with DCIS. The problem is bigger than just mammography: They say the prostate-specific antigen (PSA) test may do men more harm than good if they don't already have symptoms of prostate cancer. And they have similarly grim things to say about other widely used cancer screening tests.
Their view stands in stark contrast to the message being put out by groups like the American Cancer Society and even the federal government, which say that finding and treating tumors as early as possible is the surest way to avoid a cancer death. But a growing group of scientific heretics -- published in highly respected medical journals, working at some of the most august institutions -- strongly believe that it's time to rethink our whole approach to cancer screening.
That's because screening tests pick up many small cancers that would never have caused any symptoms. "Screening for cancer means that tens of thousands of patients who never would have become sick are diagnosed with this disease," says H. Gilbert Welch, MD, codirector of the Outcomes Group at the Veterans Affairs Medical Center in White River Junction, Vermont, and a leading expert in cancer screening. "Once they're diagnosed, almost everybody gets treated -- and we know that treatment can cause harm." Tamoxifen for breast cancer can trigger life-threatening clots in the lungs, for instance. Surgery for prostate cancer leaves 60 percent of men unable to have an erection. For that matter, some of the screening tests themselves carry risks: Up to 5 out of every 1,000 people who get a colonoscopy have a serious complication, such as a colon perforation or major bleeding.
Most people diagnosed with cancer undoubtedly see these risks as the price they must pay to avoid dying of cancer. "The reality is not so simple," says Dr. Welch. Screening tests are very good at catching tumors that would never bother us, he notes, but they're actually pretty bad at catching the fastest-growing and most deadly cancers in time to cure them. The bottom line, says researcher Floyd Fowler, Jr., PhD, president of the Boston-based nonprofit Foundation for Informed Medical Decision Making: "Screening's power to cut your risk of dying has been wildly overinflated."
How Cancer Can Fool a Screening TestThe idea that getting tested for cancer might be useless or even harmful may strike you as completely wrongheaded. After all, smaller cancers are easier to cut out. They're also less likely to have metastasized, or spread to other parts of the body -- and metastasis is generally what makes cancer deadly. Sure, it's possible for a tumor to kill without metastasizing: A brain tumor, for example, can cause devastating harm when it grows big enough to squeeze healthy tissue inside the skull. But most cancers threaten life only after a few cells break free and travel through the bloodstream or lymph fluid to set up shop in another part of the body. Once that's happened, a surgeon can no longer cure a patient by removing the tumor. And even powerful chemotherapy drugs are often unable to kill every last errant cell.
Physicians used to think that a tumor needed to get to a certain size before it would spread. But that's not necessarily so, says Barnett S. Kramer, MD, associate director for disease prevention at the National Institutes of Health. "Some tumors spread extremely early," he says. They begin metastasizing when they consist of only a few million cells, which sounds like a lot but is smaller than the period at the end of this sentence -- too small to detect with most screening tests. By the time this kind of cancer is big enough to be seen on a mammogram or other test, it's already sent seeds to other parts of the body.
The flip side of this problem is that many screening tests do a great job at catching cancers that would never have caused problems and could simply have been left alone. This notion violates most of what we think we know about cancer, says Dr. Kramer, because most of what we know is based on the tumors that cause harm. If you think of all the different varieties of cancer as making up an iceberg, cancers that cause symptoms represent only the part of the berg above the waterline. For most of human history, these were the only tumors we knew anything about: the breast cancer that had grown big enough to feel, the lung cancer that was causing shortness of breath.
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