1. Exquisite Tweets from @VPrasadMDMPH

    edoardolasalaCollected by edoardolasala

    I want to do a TWEETORIAL on a controversial topic...
    Mammographic screening
    This is the first of a MULTIPART SERIES on Mammographic screening

    This one will summarize one important paper in 2014

    I start here because, this one is a dagger
    annals.org/aim/article-ab…

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    VPrasadMDMPH

    Vinay Prasad

    TIme for TWEETORIAL PART 2 on mammographic screening.
    A MULTI-part series on this topic

    Today, we we will review this 2012 paper by
    Archie Bleyer, a fellow OHSU faculty member, and.... H. Gilbert Welch

    Sit down, It's a doozy.

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    VPrasadMDMPH

    Vinay Prasad

    As promised time for PART 3 TWEETORIAL on mammographic screening, which will cover this PROVOCATIVE paper by H Gilbert Welch at Dartmouth

    Again, the purpose of this series is just to teach, rising above the usual debates

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    Vinay Prasad

    A quick recap, in PART 1, I covered the randomized trials of mammograms according to a brilliant paper in the @AnnalsofIM
    twitter.com/VinayPrasadMD/…

    VPrasadMDMPH

    Vinay Prasad

    In Part 2, I took you through the population data, as mapped by Archie Bleyer and Gil Welch
    twitter.com/VinayPrasadMD/…

    VPrasadMDMPH

    Vinay Prasad

    In this THREAD, I will explain how Welch and Frankel estimate the probability that a woman who HAD A BREAST CANCER found by mammographic screening HAD HER LIFE SAVED (avoided dying of breast cancer) by that screening.

    But, baseline: What's your guess?

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    Vinay Prasad

    Before I explain the paper, quick background. Studies show that the public has been MISLEAD about the benefit of screening. If you survey women, you find they believe that 10 yrs of mammograms is the difference btw the Right and Left

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    Vinay Prasad

    But, BEST CASE SCENARIO, the benefit is this
    Right (no screening) vs. Left (screening)
    I say best case because this assumes that breast cancer deaths avoided are not lost via off target deaths. Not the INTENTIONAL use of 39 OR 40 in the graphic

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    Vinay Prasad

    To make their estimate Welch and Frankel do something simple
    First, they calculate what is the probability per 100k women of having a breast cancer found by mammography

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    Vinay Prasad

    It's pretty simple, its the 10 year probability of having a breast cancer (for a 50 year old woman) multipled by the percent of cancers found by mammography

    So 1910 per 100k

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    Vinay Prasad

    Next they calculate the probability a death with or without mammography
    Here they use 20 yrs (a conservative assumption aka favors screening
    So they know 990/100 k deaths in the current world

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    Vinay Prasad

    They assumed it would be 20% higher without mammograms.
    So mammograms avert 250 deaths per 100k

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    Vinay Prasad

    You gotta note that these are all very favorable assumptions for mammography. As shown in the first TWEETORIAL, there is huge uncertainty whether this 20% is true, it is, as I say, a BEST CASE Scenario

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    Vinay Prasad

    So using the best case scenario, one can make the calculation easily
    Absolute 20 year reduction in death (optimistic) divided by real diagnoses from screening = 250/1910 =.....

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    Vinay Prasad

    20% is an optimistic estimate of cause specific death reduction, and we might be better off looking more at this range, here you see the prob. a woman who HAD CANCER found on screening had her life saved, across more plausible estimates

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    Vinay Prasad

    So Welch and Frankel end with this JUGGERNAUT of a statement
    And remember this is BEST CASE SCENARIO

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    Vinay Prasad

    Why does this really matter?
    Well, it is human nature to assume that HAD IT NOT BEEN FOR <whatever you did in your life> you would be <in some very bad state of being>

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    Vinay Prasad

    This is the same cognitive error that keeps residency work hours barbaric because HAD IT NOT BEEN FOR <my long hours> I would be <a bad doctor>

    And pretty much every other entrenched, unsupported status quo thing you can imagine

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    Vinay Prasad

    With cancer screening, Welch and Frankel are wise to note the power of the anecdote seems to trump all data and all reason, they write:

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    Vinay Prasad

    Critics can view this paper as TOO PESSIMISTIC or OPTIMISTIC-- I am fairly sure it is too optimistic, but the major virtue of the paper is that it tries to get us to start using our best thinking to understand a question rather than resort to simple, false sentiments

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    Vinay Prasad

    Sadly, this is a lesson we desperately need in other topics, for instance cancer exceptional or super responders, where one must interrogate whether the outcome is truly due to the drug or was it due to the biology/ person
    drive.google.com/file/d/1Ba8m8l…

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    Vinay Prasad

    Ahh, but that's a different topic for another series.
    But, don't fret, there will be a PART 4 to mammographic screening TWEETORIAL series.

    Final question: Was this helpful?

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    Vinay Prasad