Tuesday, November 17, 2009

Does number needed to treat help with rational decision-making?

Here is the perfect illustration of how irrational and emotional the issue of breast cancer is. Take the current maelstrom over the USPSTF's new screening mammography recommendations, which now advise against routine screening for women between the ages of 40 and 49 and change the recommended interval for women 50 to 74 years old from yearly to biennial screening. Let's focus on the number needed to invite (a diagnostic test's analogue of the number needed to treat, NNT). The NNT of mammography for a woman in her 40s is nearly 2,000, meaning that we need to screen 2,000 women to prevent 1 breast cancer death. Similarly, among women in their 50s, this number is about 1,300.

Let's not even talk about what the implications of over-diagnosis and over-treatment may be in all these women; I have written about this in the past here and here. Let's just focus on costs. An average cost of a mammogram is ~$100. So, multiplying the 2,000 NNT by $100 yields $200,000 per life saved. Again, if this were the only cost (and again, we are staying away from costs of repeat testing of false positives, invasive diagnostic testing and potential over-treatment and its attendant complications), I would say that it might be reasonable, especially when you take into account the number of years that can be saved for a woman in her 40s.

Now, let's look at the only therapy on the market that reduces mortality in patients with severe sepsis, drotrecogin alfa (activated). Its NNT is 16. That's right, it takes treating 16 patients to prevent 1 sepsis death. Given that a course of this drug costs ~$10,000, the cost to save 1 life is $160,000, or not that different from screening mammography in the 40-49 age group. Though the drug cost is 2 logs higher than that for mammography, the total population is about 2 logs less, so the total costs may be comparable. Yet, there is no battle going on for the use of drotrecogin alfa, and is has been all but abandoned by the ICUs in the US, mostly due to its expense.

So, without making any kind of a value judgment or a politically motivated statement, is this not a double standard? Is this not irrational and selective? Is this a result of a disease with a strong lobby versus one that does not have a patient advocacy group (mostly because 50% of these patients die in the hospital)? Or is it that mammography is perceived as prevention while drugs are disease treatment?

I am really not sure what the answer is to this apparent double standard. I also will refrain from proselytizing about the willingness to pay and whose money and the potential harm and even death due to over-diagnosis and over-treatment. But people, we do need to confront our irrational demons of inconsistency. On the other hand, if we cannot make these allocation decisions rationally as individuals, don't you think we would benefit from a body whose sole purpose it is to do this transparently and in an evidence-based manner?            

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