Is It a Life or Death Question? Cancer Researchers Disagree
Donald A. Berry, a member of the Physicians Data Query panel, is chairman of the department of biostatistics at M.D. Anderson Cancer Center in Houston.
Question: Were you surprised by the controversy?
Answer: In a way, I was. Our deliberations had been low-key. We proposed a modest change in the mammogram guidelines because we found that the scientific evidence that mammography is beneficial is pretty weak. Women have been oversold on screenings because there’s so much anxiety out there about breast cancer. Consequently, anything that might help is viewed with great joy.
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Q: What prompted your committee to review their guidelines?
A: Our conclusions about the benefits of mammograms were based on the outcomes of seven studies that have been conducted around the world. We knew these studies weren’t perfect but there was an article a few months ago in a scientific journal [the Lancet] which detailed some serious flaws in this research. Our subsequent review agreed with some of their critiques, and there was certainly a smoking gun or two, in terms of potential biases in these studies.
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Q: So your committee concluded there is no benefit to having mammograms?
A: We went through lengthy discussions, and the issue is quite complicated. But the key question is: Does having regular mammograms reduce mortality? And we decided that was uncertain--and that’s our bottom line. No definitive studies have been done that really prove mammograms are beneficial.
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Q: If there is no benefit, then why do doctors continue to enthusiastically recommend that women get them?
A: Some [people] don’t appreciate the importance of biases in making observations in screening programs. What they observe is that for women whose breast cancer is identified from mammograms, the prognosis is extraordinarily better than for those whose cancer is detected from a physical breast exam [by their doctors, a procedure called palpation]. But it doesn’t logically follow that a mammogram is what made the difference.
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Q: What are these biases?
A: The first is the lead time bias. What that means is that you can detect an aggressive breast cancer earlier with a mammogram than you would by mere palpation. So instead of dying three years after being diagnosed, patients might live seven more years. But all you’re really doing is moving the goal posts, and these women didn’t survive longer than they would have without the mammogram. They were just diagnosed earlier.
The other key bias is length bias, which is more subtle. Mammograms tend to detect the smaller, slower-growing cancers that take longer to kill women. Or the tumor might have grown so slowly that they died of something else, and the cancer might not have been discovered otherwise.
Palpation, in contrast, tends to identify the faster growing, more aggressive cancers. These tumors often don’t show up on routine mammograms because they may develop between screenings. As a consequence, since physical exams tend to find the more dangerous tumors, mammograms--which pick up the less risky cancers--look good in comparison.
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Q: How do you account for the difference in the findings of your committee and those of the U.S. Preventive Services Task Force, which based their recommendations on the same research?
A: Two groups looking at the same data can come to different conclusions. On the face of it, It looks like PDQ views it one way and the task force views it another. But we’re really not that far apart in terms of our conclusions. We rated the quality of the mammogram studies as low, while they rated them as fair, which is not that different. Their conclusion is, essentially, “Sure, why not? It can’t be bad and it might be good.”
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Q: Do you think the push for screenings lulled women into a false sense of security--that by getting regular tests their cancers would be cured?
A: I think everyone is well-meaning. But we still don’t know if a small cancer that’s picked up in a routine screening has already metastasized [spread beyond the breast], and we still can’t identify which tumors are more dangerous. So there’s always the potential for unnecessary or ineffective treatment.
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Q: In the meantime, given all this conflicting information, what should women do?
A: The truth is we don’t know. Women should find out about the uncertainties associated with mammography, such as the risks of false positives, and unnecessary surgery, as well as the inconvenience and expense of getting screened. They should balance this against the benefits, which are really quite modest even if you believe the test results at face value.
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Q: Are you comfortable with the idea that some women who decide not to get mammograms based on your committee’s recommendation might have breast cancer that might have been better treated if detected sooner?
A: I’ve thought long and hard about this and I don’t feel uncomfortable at all.
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Q: What do you tell your own family?
A: I tell my wife not to get screened. But she ignores me.
