It's hard to have a blog about evidence and medicine without commenting on the changes to the USPSTF's breast cancer screening guidelines.
At a first pass, it's worth pointing out that a lot of academic primary care physicians have been wondering what the USPSTF was thinking when they published their 2002 guidelines recommending mammography for women in their 40s. Yes there may be some small benefits (and lots of harms), but this is just the sort of thing that the USPSTF can usually be relied on to not recommend -- look for instance at what they recommend for prostate cancer screening or lipid screening for women. As a result, there were lots of insinuations that the USPSTF had caved to political pressure in making the mammography recommendation. Perhaps others know more about that one way or the other.
Now they've backed away from that recommendation, going from a favorable to a negative recommendation for mammograms. The overall issues aren't actually that complex: if you imagine 1000 women in their 40's getting mammograms yearly for 10 years, the best estimates are that you will cause more than half of them to need repeat mammograms for concerning findings, and will cause nearly 200 to get breast biopsies, while only preventing 2 deaths from breast cancer.
What is remarkable is the firestorm that has been set off. When I present these data to women patients in their 40s (in a way that I think is fair to both sides of the argument), I've found that approximately half want mammography and half want to wait until they turn 50. Individual patient values and preferences heavily influence the decision. The USPSTF takes this into account by recommending against routine mammograms in the 40s, but states that a decision to screen should take consider an individual woman's values. All in all, not that unreasonable a position as far as I'm concerned.
I think, though, that the USPSTF's way of grading recommendations is awkward in general and may even have contributed to the confusion over their 2002 and 2009 recommendations. The evidence base didn't substantially change over that time frame, but the recommendations did, and that opens them to attack.
(Here I need to make one of the only conflict of interest disclosures I should ever need to mention on this blog: one part of my work is as a medical editor, and in our publication we use GRADE.)
That out of the way, the USPSTF grading scheme is unusual in the way that it combines strength of recommendation and quality of evidence into a single value (a letter grade). To me, this overloading causes problems. For many of the recommendations that USPSTF gives a grade of I to (insufficient evidence), GRADE and a number of other schemes would note the low or moderate quality of the evidence and still allow a guideline committee or other recommending body to make a suggestion about what a clinician should do.
When there is enough evidence to make a suggestion (a "weak recommendation" in GRADE parlance), GRADE explicitly deals with the need for considering patient values and preferences. If, instead of being used to this single letter grade from USPSTF, we were used to seeing evidence and recommendation divided, I'm not sure the recommendation change would have caused quite so much trouble.
The USPSTF recommendation, cast into GRADE style, would likely have read:
For most women ages 40 to 50, we suggest not performing yearly mammography (Grade 2B). Women who are willing to accept a high risk of false positive mammograms and a high risk of unnecessary biopsies in return for a small mortality benefit may reasonably prefer annual mammography starting at age 40.
Would a recommendation written this way have caused the same firestorm? I'd be interested in what others think about this. Would it have caused a firestorm if the 2002 recommendation had said the opposite?:
For most women ages 40 to 50, we suggest performing yearly mammography (Grade 2B). Women who are unwilling to accept a high risk of false positive mammograms and a high risk of unnecessary biopsies in return for a small mortality benefit may reasonably prefer annual mammography starting at age 50.
You can see how easy it is to split the unchanged evidence base from the change in what you are suggesting for the majority of women (based on a guess about their values and preferences) when using GRADE. I think such an approach is more transparent than that used by the USPSTF, and keeps the focus where it belongs in a situation like this -- on the benefits, risks, and burdens that influence the decisions for individual patients and for society.
I'll write more about the methods of GRADE, including its strengths and weaknesses, down the road. I do want to say that while I don't like the grading scheme used by USPSTF, I think they mostly do a wonderful job of staying true to the evidence as they present their guidelines. We should all hesitate to recommend screening tests in the absence of solid evidence showing benefit, and the USPSTF can almost always be counted on in this regard.