No one doubts that in international comparisons of cancer care, the US spends more than any other country. Whether this higher spending produces commensurate health benefits, however, is far from certain.
In the April 2012 issue of Health Affairs, Philipson et. al. make an intuitively persuasive observation, one which they summarize in their recent Health Affairs Blog post (authored by Goldman, Lakdawalla, and Philipson): “We find that survival after diagnosis rose more quickly in the U.S. than the E.U.”
Given this observation, they go on to make an inference, namely that the US gets value from it additional expenditures on cancer care. It would be nice were the world so simple. But it’s not.
Early Detection And Overdiagnosis Biases
Philipson et. al. fail to appreciate the powerful early detection biases associated with survival comparisons both across time and place. While they do acknowledge that advancing the time of diagnosis can spuriously elevate survival without any delay in the time of death (the so-called lead time bias), they assert in their blog post:
The possible existence of lead time bias is not, on its own, reason to question our conclusions, because we examine changes in survival over time. This approach eliminates such bias in most cases.
But that would only be true if lead time was stable across time and place, or changing in exactly the same manner from country to country. Given the enthusiasm for opportunistic screening in the United States — not to mention the high rates of cross-sectional imaging that add to incidental cancer detection — such an assumption is simply not credible.
Moreover, as pointed out in a letter by Dr. Keith Marton, Philipson et. al. ignore the yet more powerfully misleading effect of making cancer diagnoses in patients not destined to die (or experience symptoms) from their cancer (the so-called overdiagnosis bias). Overdiagnosis can have a powerful effect on survival rates, even if no one has their life prolonged.
To understand why, imagine a country in which 1,000 people are found to have Cancer X because of symptoms (they all have progressive cancer). Five years after diagnosis, 500 are alive — producing a five-year survival rate of 500/1000 or 50 percent — and 500 have died.
Now imagine the same country with lots of cancer screening and/or incidental cancer detection. Perhaps 2,000 would be given a diagnosis of Cancer X, although 1,000 would actually have indolent forms and not be destined to die from their cancer. Five-year survival will increase dramatically, to 75 percent, because the 1,000 people with indolent cancer appear in both parts of the fraction: 1,500/2,000. But what has changed? Some people have been unnecessarily told they have cancer (and may have experienced the harms of therapy), and the same number of people (500) still died from Cancer X.
Read the full article here.
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