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    Thursday, October 19, 2006

    Questioning the Conventional Wisdom: The Cochrane Group, a very good source of unbiased evidence based medicine, says that mammograms may do more harm than good:

    Concerns have been raised that breast cancer screening might lead to some women undergoing unnecessary treatment.

    Researchers looked at international studies on half a million women.

    They found that for every 2,000 women screened over a decade, one will have her life prolonged, but 10 will have to undergo unnecessary treatment.

    My experience has been that the false positives and unnecessary procedures have gone up dramatically since radiologists began to use computers to double-check their mammogram readings. But, my patients never express regret in being over-treated. The dangers of false positives are a tough sell. Most people want everything done just to make sure they're OK and that nothing gets missed. The problem is that those unnecessary procedures cost money. Most of the time, it's the government's or the insurance company's money, so no one cares. Until their premiums or taxes go up. Maybe with each insurance premium increase or tax raise, the public should get an itemized bill explaining exactly why the increases are necessary, and where the money is going.

    The Cochrane evidence is here.

    posted by Sydney on 10/19/2006 09:42:00 AM 6 comments


    Most of the pressure on women to get mammograms comes from breast cancer charities, the American Cancer Society, and articles in women's magazines. All of which strongly, repeatedly warn women to get regular mammograms, and all of which strongly, repeatedly declare that mammograms save lives.

    And people wonder why women go for regular mammograms.

    By Anonymous MR, at 5:01 PM  

    Women might not object to false positives, but how many of them know about overdiagnosis? How many of them understand that overdiagnosis increases incidence and that their chance of being diagnosed with cancer is higher if they are screened? How many women are told the real probability they personally benefit?

    Google on mammograms. It is not only ACS and charities: clinic websites, doctors web pages, "talk to the doctor" boards -- all have the same message: have a mammogram. If you choose not to, you are labelled irresponsible.

    Screening is not presented to us as a choice. It is presented to us as an obligation. So how can anybody wonder why women do it?

    By Anonymous Diora, at 10:08 PM  

    And it will get worse!

    Lately, radiologists are pushing MRI mammograms, touting a three fold increase in sensitivity. True but, like other tests, an increase in sensitivity comes at the price of more false-positives. In this case, about FIVE TIMES more biopsies for benign lesions.

    In med school, I was told that a normal patient needs more testing. Exactly.

    By Anonymous EM, at 1:54 PM  

    I have always been in favor of analyzing the end results. Overtreatment generally doesn't kill someone, but breast cancer definitely can. The authors could build upon this study by seeing how many years of life were saved by mammography (they say "lives were prolonged," but we don't know by how much). I think they probably have the data to do that.

    They could also look at the costs of treatment (and over treatment) compared to the costs of no mammography and balance that against years of life saved- but cost/effectiveness analysis always makes people queasy becasue ultimately, you're assigning a dollar value to a year of life.

    So I'd say they have gotten a good start on the question of the value of mammography, and with a few more calculations, they could really help put the issue to rest (scientifically, at least).

    In past studies showing no benefit, the people that disagree sometimes state the equipment wasn't state of the art, or the patients weren't getting mammos often enough. This may be true, but it also sounds a little self-serving, to me, becaue it implies that we should devote even more resources to their cause.

    One weird thing- the BBC article said,

    But they also discovered it was diagnosing woman with breast cancer who would have survived without treatment, meaning they were undergoing unnecessary chemotherapy, radiotherapy or mastectomies.

    That is the weirdest statement I ever heard- or else there was a lot of divine intervention going on.

    By Anonymous dani, at 5:19 PM  

    "But they also discovered it was diagnosing woman with breast cancer who would have survived without treatment, meaning they were undergoing unnecessary chemotherapy, radiotherapy or mastectomies."

    That is the weirdest statement I ever heard- or else there was a lot of divine intervention going on.

    Dani, this statement is about overdiagnosis not divine intervention. There are more screened women that are diagnosed with cancer than non-screened women.
    Women who are not screened never quite catch up. Some percentage of these extra cases represent "overdiagnosis": something looks like cancer under the microscope, but would never have spread outside the breast if remained undetected. So, women who get diagnosed with one of these cancers undergo treatment unnecessarily because without detection and treatment they would've lived their full lives not ever knowing they had cancer.

    The trouble is there is currently no test to detect only the "real" cancers - i.e. those that behave like cancers and not just look like cancers under the microscope.

    Estimates of overdiagnosis vary - from as low as 5% to as high as 50%. The authors of the referenced article estimated it at 30%. This means quite a lot of women would've never become cancer patients without mammograms. All of them go throw treatment unnecessarily. The trouble is - there is no way to say whose life is saved and who suffered side effects from the treatment, maybe for life unnecessarily.

    em, I am surprised you say that extra sensitivity leads to more false positive but forget to mention that it also leads to more overdiagnosis. Any reason for it?

    And you are wrong that overtreatment never kills: surgery has risks, radiation may increase risk of heart desease; in rare cases it can lead to sarcoma. The risks are small and well worth it if the treatment is life-saving, but if it is one of those "overdiagnosed" cases it is quite another matter. Also if the probability of benefit is very small even this small risk matters.

    By the way, the studies that found no benefit are CNBSS-1 and -2. The equipment in these studies was no worse than the equipment in other studies - their detection rate was just as good. It was also a more recent study compared to others - 1980s rather than 1960s, so it was done at the time of better treatment. Many reviewers (like PDQ -- look up NCI website) consider it one of better quality studies. It was also the only study that compared mammograms to clinical breast exam as opposed to mammograms to nothing in other studies. And one other thing - it is the most reviewed and scrutinized of the studies. Some of the other studies that show higher benefit never made their data available to independent review. Don't you think it is interesting that there is no improvement in newer studies compared to older studies?

    As far as putting the matter to rest - I think the women are not stupid. They should be told the chance their life would be saved, but they should also be told about overdiagnosis and false positives and the probability of both. They should have the right to choose if a small chance of saving their life is more important for them then the higher chance of becoming a cancer patient as well as biopsies.

    By Anonymous Diora, at 7:12 PM  

    Hello, I'd like to present you interesting articles about this disease:
    Breast Cancer
    Breast Cancer: Trends and Incidence
    Breast Cancer: Risk Factors
    Breast Cancer: Effective Universal Preventive Interventions
    Breast Cancer: Effective Selective Preventive Interventions
    Breast Cancer: Effective Indicated Preventive Interventions
    Breast Cancer: Practice and Policy Implications
    Breast Cancer: Future Directions

    By Blogger Jason Walker, at 3:45 AM  

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