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    Wednesday, March 28, 2007

    Hunting Cancer: The news this morning is that magnetic resonance imaging should be used to screen for breast cancer:

    Women who face a high risk of breast cancer should undergo annual magnetic resonance imaging to detect the disease rather than conventional mammograms, the American Cancer Society will announce today, marking the first time that leading radiologists have advocated the routine use of MRI scans as a screening test.

    I would have more confidence in those recommendations if they didn't come from radiologists - who get paid more to read MRI's than mammograms. The recommendations are only for women at high risk - those with genetic mutations for breast cancer, those who have had breast cancer, and those whose mothers or sisters have breast cancer. And yet, they seem to be casting the net a little more widely in the article:

    Unfortunately, there is no easy way for many women to determine on their own whether they are in the high-risk group, the size of which is also uncertain. Women can get blood tests to find known cancer genes, including the BRCA1 or BRCA2 mutations, whose carriers face a lifetime cancer risk of up to 65 percent. But researchers believe there are others that have not yet been confirmed. As a result, doctors must estimate women's cancer risk through a detailed review of their family medical history.

    "There are women who are unaware they are at high risk because they don't have obvious family history," said Smith. "It takes a genetic counselor to tease out the risk."


    Hmmm. Are there enough genetic counselors to tease out the risk of every woman in the United States? Maybe in Boston, but not in Dubuque.

    And if MRI's are so great for those at high risk, why aren't they recommended for those at average risk?

    "The real question . . . is whether we should be screening all women with MRI," said Kopans, noting that nobody knows how many of the 40,910 breast cancer deaths expected this year in the United States could be prevented with MRI. "What if MR screening could knock it down by 90 percent? Is that worth $800 apiece to do MR screening for everyone? These are very important questions, and somebody is going to have to bite the bullet and do a very large, expensive study" to find out.

    Experience tells us, that here in the United States, no sum is too large to save one or two lives. We adopted the universal chickenpox vaccine to avoid 100 deaths a year. But here's the rub- finding those cancers early doesn't necessarily translate into saving lives:

    In addition, Cancer Society officials noted that there is no proof yet that all the extra cancers detected by MRI translate into longer lives for patients. The life-extending benefits, they said, will only become clear if women are followed over a longer time.

    As of this writing, the details, as published in the Cancer Society's journal, are still embargoed, but their press release provides some more detail regarding who they consider at risk:

    * they have a BRCA1 or BRCA2 mutation

    * they have a first-degree relative (parent, sibling, child) with a BRCA1 or BRCA2 mutation, even if they have yet to be tested themselves

    * their lifetime risk of breast cancer has been scored at 20%-25% or greater, based on one of several accepted risk assessment tools that look at family history and other factors

    * they had radiation to the chest between the ages of 10 and 30

    * they have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome, or may have one of these syndromes based on a history in a first-degree relative


    There's no doubt that MRI's are better at finding small tumors than mammograms. That's true in general when MRI's are compared to conventional x-rays. The question remains whether finding them that small is worthwhile.
     

    posted by Sydney on 3/28/2007 07:45:00 AM 3 comments

    3 Comments:

    Great post. Clearly this is a science in evolution and a damned if do, damned if don't scenario. MRI's cost money, so do missed cancers. Both are scarry. Perhaps mammogram technology needs looking at - if those annual tests were more accurate, and for more types of breasts, women would worry less about having something missed. 20% of women a year have cancers missed on mammograms - that's no small amount.

    By Blogger DrGwenn, at 12:04 PM  

    Good post. I'd have liked to see more discussion about the potential of overdiagnosis with MRI - a serious potential harm that is often ignored in the articles. It may be unimportant to women at very high risk, but it surely is for the rest of us.

    Doctors love to say how women don't care about overdiagnosis. I think the more accurate statement would be is that they don't know it exists, or don't understand the implications. It is rarely discussed. Very few understand how it increases their chance of becoming a cancer patient.

    As far as 20% mentioned in the post above - drgwenn doesn't know in which percentage of these cancers earlier detection would've make a difference. In some of this cases, when the cancer was found later it was still small and treatable as with this woman, who is actually glad of extra 8 "healthy" years, some of the others may have killed anyway. You have to show mortality reduction which is the only real measure of test effectiveness.

    By Anonymous Diora, at 12:29 PM  

    My wife participated in a study at the University of Minnesota to correlate MRI readings to breast cancer biopsy results.

    Her mammogram showed that she probably has breast cancer.

    Her MRI should that she did not.

    Her biopsy showed that she did not have breast cancer.

    Maybe MRIs wll replace biopsies in the future and that would save money.

    By Blogger Jake, at 3:36 PM  

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