Wednesday, November 25, 2009

Breast Cancer Screening and Evidence-based Medicine


In case you’ve been in a coma for a while, the US Preventive Services Task Force (USPSTF), a federally-funded-but-independent group of scientists who evaluates the evidence regarding preventive care, has announced new guidelines on screening for breast cancer. It has generated an amazing amount of comment, from physicians, patients, advocacy groups, politicians, and journalists. Every possible position on the issue, from thoughtful and balanced to alarmist and opportunist, has been taken and published by someone. For a quick review of articles just in the New York Times in the last few days we have:

November 17:
Panel Urges Mammograms at 50, Not 40”
November 18:
New Mammogram Advice Finds a Skeptical Audience”,
Many Doctors to Stay Course on Breast Exams for Now”
November 19:
Screening Policy Won’t Change, U.S. Officials Say
Columnist Gail Collins: “Breast Brouhaha
November 20:
Kevin Sack, News Analysis: “Medical Science and Practice in Conflict
Mammogram Debate Took Group by Surprise

Therefore, the wise course might be for me to stop here, let you read everyone else, and not get involved. Of course, I won’t. Let me start by discussing the discovery, use, and application of evidence in medicine, and in particular with the USPSTF.

Disclaimer: I don’t work for, or have any relationship, financial or otherwise, with USPSTF, but I do believe that the responsible practice of medicine requires keeping up with the evidence and changing practices as new information becomes known; it should not be a “faith-based” effort.

Medical evidence for anything, including appropriate preventive services, gathers slowly. Studies are first done on high-risk populations, then later on average or low risk. Depending on the variables looked at, and the population studied, different information can emerge. Rarely (but sometimes) is the data from one good study on the same population directly opposite that of previous studies; more likely it will be similar, but might be of a greater or lesser degree of magnitude. Or just different enough to tip the risk/benefit balance. Because virtually never is anything – a treatment, a diagnostic test, a preventive activity – all good or all bad. There are benefits, real or potential, and risks, of varying degree. As new evidence accumulates, it tends to move the scales, or the seesaw, more down or up on one side or the other. Usually not enough to drop one end to the ground, but sometimes enough to tip the balance. And new studies are being done all the time, and it is not only hard to keep up, it is hard to assess the changes in risk. But it must be assessed, because it would be wrong to just keep doing what you were doing when the evidence changes.

That is the incredibly valuable service that the USPSTF has been providing since it was first convened in 1984. Evaluating, the existing studies and making recommendations – to clinicians – on what they should discuss with their patients. They are not really for patients, although this seems to be where much of the confusion is. Much of the coverage is about individual women trying to decide what to do – or reacting “against” the recommendations. The Times article cited above, “Many Doctors to Stay Course on Breast Exams for Now”, includes this: “Patients are already trying to figure out what the recommendations mean.” It means they should discuss them with their health care provider.

USPSTF assigns both a grade and a level of certainty to its recommendations. The grades are A, B, C, D, and I, and the levels of certainty are high, moderate, and low, and are described at the USPSTF website, at When the grade is A or B, the procedure is recommended to clinicians in practice; when the grade is C it is generally not recommended, but there may be individuals or situations in which the benefit would exceed the risk; when it is D, it is not recommended. A grade of I means there is insufficient evidence to assess whether there is net benefit.

USPSTF is not the only group that makes recommendations. Many medical professional organizations and advocacy groups (such as the American Cancer Society and the American Heart Association) also make recommendations. However, the USPSTF is independent and has no “dog in the fight”, no financial or emotional attachment to an outcome. For example, after these recent recommendations were announced, suggesting most women start receiving mammograms later, and have them less often, the American College of Radiology (ACR) announced its disagreement with them. I’m sorry, but the fact that radiologists have an obvious financial stake in doing more mammograms has to make their opinion more suspect.

Certainly doing fewer mammograms will save money for insurers (including the government, for Medicare patients). In the current climate of our debate on health reform, some have seen these recommendations as an effort by these insurers to save money, and others have noted that, because of this, the timing of the announcement was “unfortunate”. However, unlike the ACR, the members of the USPSTF have no financial stake in their truly independent recommendations. I, for one, absolutely consider them to be the most valid source of independent analysis and advice.

What about these specific recommendations? They make sense to me, and are supported by the evidence. The recommendation that mammography begin at 40, rather than 50, only dates back to 2002, and was controversial at that time.
“In 2002…,” reports the Times in Panel Urges Mammograms at 50, Not 40, “When the group recommended mammograms for women in their 40s, some charged the report was politically motivated. But Dr. Alfred Berg of the University of Washington, who was the task force chairman at the time, said ‘there was absolutely zero political influence on what the task force did.’ It was still a tough call to make, Dr. Berg said, adding that ‘we pointed out that the benefit will be quite small.’ In fact, he added, even though mammograms are of greater benefit to older women, they still prevent only a small fraction of breast cancer deaths.” In the last 7 years more studies have come out, which have weakened the relative benefit to risk ratio for women between 40 and 50 who are at average risk for breast cancer.

In addition, the body of evidence does not suggest that there is significant additional benefit to screening every year rather than every two years. It also recommends against teaching self-breast examination (not against women doing it) – a “D” recommendation -- because there is good evidence from large population studies that it offers no advantage death or morbidity from breast cancer. Continuing screening of women over the age of 74, and doing clinical breast examination (by a physician or other clinician) in addition to mammography get “I” – insufficient evidence recommendations.

In the news analysis cited above, “Medical Science and Practice in Conflict
Mammogram Debate Took Group by Surprise”, Kevin Sack notes that “The backers of science-driven medicine, with its dual focus on risks and benefits, have cheered the elevation of data in the setting of standards. But many patients — and organizations of doctors and disease specialists — find themselves unready to accept the counterintuitive notion that more testing can be bad for your health.” But it certainly can be.

More, it should be obvious, is not always better, not only with fatty foods and salt, but with screening. The risks of unnecessary (read: too often for the risk level of the woman under consideration) mammograms is more than anxiety for false positives. It is also biopsy for false positives. And sometimes complications. And radiation exposure, which is not insignificant, and is, as we know, linked to causing cancer. Think: men get breast cancer also, but not at the rate that women do (about 1%). We do not screen men, because the risk/benefit ratio is way over to risk. Let me make clear that all of this discussion is about screening; by definition, someone who has NO symptoms. No lump, no discharge, no skin dimpling. They are not about diagnostic mammograms – examining someone with symptoms or physical findings, or a previous abnormal mammogram, and certainly do not apply to follow-up of people who have had breast cancer.

In “Many Doctors to Stay Course on Breast Exams for Now”, Dr. Annekathryn Goodman, director of the fellowship program in gynecological oncology at Massachusetts General Hospital, says “It’s kind of hard to suggest that we should stop examining our patients and screening them….I would be cautious about changing a practice that seems to work.” I hope that is not what she meant. What “seems to work”, while intuitively attractive, is not always correct. That is why we have independent bodies such as USPSTF continually examining the evidence.

No comments:

Post a Comment