In a recent Health Affairs paper, we documented that the United States has a significant survival advantage over much of Europe when it comes to cancer: 1.8 years for those diagnosed during our study window. Furthermore, we showed over a 17-year period that this gap had widened, not narrowed, and that this widening was more valuable than traditional health valuation approaches suggest. As a result, we argued that the additional spending in the United States was ‘worth it.’
These results have generated a lot of controversy, and even some criticism. We understand the controversy given the impression that US health care spending is too high. However, we find the criticism both irrelevant and misguided, both qualitatively and quantitatively.
First, some critics have argued that we should have looked at mortality rather than survival. That is, we should have measured how many people have died from cancer, rather than how long people who are diagnosed with the disease live with it. There is an important distinction, as we note later. Some have argued that survival estimates suffer from a “lead-time” bias because the United States was differentially diagnosing cancer earlier.
Our Paper Looks At Mortality Estimates As Well As Survival Estimates
This criticism is somewhat puzzling since we also examine mortality trends in our paper, and the same story holds. As discussed both in the main paper and an extensive technical appendix, we examined trends in cancer mortality rates over a similar period – 1982 through 2005 – using the WHO Cancer Mortality Database. The mortality results for the United States for the most controversial cancers (prostate and breast) fell relative to the EU. The results implied that if the US had progressed in its cancer care at the same rate as the EU over this period, there would have been 87,000 additional breast cancer deaths and 222,000 prostate cancer deaths. These correspond to a gain in life expectancy of 1.8 years for prostate cancer patients and 0.8 year for breast cancer—similar to our survivorship analysis. The bottom line is that looking at mortality also supports our finding of a widening gap between the United States and the European countries we investigated.
So why did we analyze survivorship rather than population cancer mortality? Naturally, mortality and survivorship convey equivalent information if one conditions on diagnosis. However, at a population level, mortality also depends on the number of people who get cancer each year (incidence). So mortality – unlike survival – is sensitive to underlying trends in behavior affecting cancer that have little to do with the health care system. For example, if the United States stopped smoking at a greater rate than the EU, we would expect mortality to fall, but we should give credit to public health efforts rather than health care delivery. Furthermore, mortality analyses can itself be subject to bias due to changes over time in attribution of cause of death.
Ultimately though, people with cancer—and their physicians—are most concerned about their survival chances once they are diagnosed. While mortality rates in the population may be a focus of epidemiological research, they are not the statistics of greatest interest to those diagnosed with cancer. Once diagnosed, a patient and her physician care more about how long she will live—hence our choice of survival as the primary endpoint. Put another way, researchers do not abandon measuring survival in oncology trials because there is a well-recognized issue of attrition bias. The bottom line here is that one wants to compare differences in health care treatment, survival and not mortality is the appropriate outcome.
Lead-Time Bias Is Not A Plausible Explanation For Better US Survival Rates
So we are left with survival conditional on diagnosis as the substantively important endpoint. We find that the US has gained half of one year over the European countries over the study period. This gain comes at a cost of $17,000, suggesting a cost of a life year of about $38,000. Since the typical value of a life year is $150,000 in the United States, lead time bias would have had to contribute 75 percent of the additional gain in the US to reverse our conclusion.
So is 75 percent lead time bias possible? First of all, it should be noted that we are not saying the United States does not diagnose earlier. In fact, this motivated our approach to look at trends in the United States relative to Europe—that is, a ‘differences-in-differences’ approach. Thus, lead time bias would not only have to exist (which we readily admit), but it would have had to have dramatically expanded by more than 75 percent in the United States relative to Europe over the study period.
The quantitative evidence suggests it did not. In previous work, we have shown that earlier diagnosis was only responsible for a small fraction of the overall gains in survival conditional on diagnosis, the rest being attributable to better treatment conditional on stage of diagnosis. Preston and Ho draw a similar conclusion. Moreover, using the US CEER data we have shown that US cancer survival gains from 1988 to 2000 are primarily due to treatment advances, rather than earlier detection. For 5 different tumors, changes in the probability of early detection were relatively small, less than 15-20 percent, compared to changes in survival at every given stage.
In other words, in the US CEER data, moving the distribution to earlier stages contributed a small share of survival compared to the rise in survival for each stage. This suggests to us that the criticism of lead-time bias in our work is substantively misguided. Even when one accounts for lead-time bias in a quantitative way, it is very unlikely to affect our conclusion that the US cancer spending was worth it.
The UK Was An Outlier In Change In Population Cancer Mortality
Usually the loudest critics of any study are those whose own findings disagree. Our case is no exception. Past research by some of our critics has shown that the United Kingdom has made faster progress in reducing mortality over recent years looking at breast cancer. However, this gives a biased picture, since the United Kingdom was a clear outlier in the change in population cancer mortality, as shown in the exhibit below. (Click to enlarge.) Other countries in the EU did not experience the rapid declines in breast cancer mortality seen in the UK. Furthermore, declines in mortality in the UK for other cancer types have been less rapid than in the US, notably for prostate cancer. Ignoring the issues with measuring population mortality, this evidence seems less representative to the larger set of cancers and countries in the EU that our study considered.