Enhancing Cancer Registry Data to Promote Rational Health System Design

Those of us in large chaotic health-care systems, like that in the United States, look with particular interest at the experience in smaller more contained health systems, like that in The Netherlands, to glean how we might apply rational principles to organizing care delivery. In classical epidemiology, we have learned a tremendous amount by examining the experiences of those in The Netherlands and other countries, such as Scandinavia, who couple meticulous records on the vital status and health of their populations with high-quality cancer registries. Similarly, in clinical epidemiology and health services research, we gain enormously from evaluating the experiences of other health-care systems with different models of care delivery. It is therefore with great interest that we examine the study from The Netherlands by Vernooij et al. ( 1 ) that compares delivery of ovarian cancer care among generalized, semispecialized, and specialized hospitals. The authors sought to obtain information as to whether ovarian cancer patients who receive their care in specialty cancer hospitals have superior survival outcomes compared with those who receive their care in semispecialized or general hospitals. Using tumor registry data, they compared survival outcomes for the 40% of Dutch women who received ovarian cancer care at general hospitals with that of the 40% who received care at hospitals with some cancer expertise and the 20% who received care at specialty cancer centers. They found a 5-year relative survival of 38% at general hospitals, 39.4% at semispecialized hospitals, and 40.3% at specialty hospitals. They relied on 5-year relative survival — that is, the ratio of the observed survival to the survival that was expected based on the age- and period-specifi c mortality of the general population — as a proxy for cancer-specifi c survival, which is not reliably tracked by the cancer registry that they used. The limitations of the analysis by Vernooij et al. (1) and by others ( 2 – 4 ) are those that are inherent in their data source — population-based tumor registries. Although tumor registries in The Netherlands and elsewhere collect meticulous high-quality data on cancer site, histology, and stage, several critical pieces of information that infl uence both choice of treatment and cancer outcomes are missing. In particular, there is no information about comorbidity or performance status. Consequently, it is exceedingly diffi cult, if not impossible, to determine whether the survival differences reported are due to differences in the quality of care or to underlying systematic differences in the characteristics of patients who seek care at general vs specialty hospitals. This potential for selection bias is the bugaboo of scores of articles on regionalization of specialty cancer care as well as the related voluminous literature on volume – outcome relationships in cancer surgery. In the analysis of Vernooij et al. (1), we note that patients treated at general hospitals were an average of 5 years older and were substantially less likely to undergo primary surgical reduction or to receive systemic chemotherapy than those treated at more specialized centers. It is of course not possible to know whether the patients who did not undergo debulking surgery and chemotherapy would have received these interventions had they gone to a specialty center or whether these interventions would have improved their outcomes. However, both the age of the patients and the treatment differences strongly indicate that Dutch ovarian cancer patients who seek care at specialized hospitals have different characteristics from those who seek care at general hospitals. This potential for confounding makes it impossible to know whether the superior outcomes at specialty centers are a result of the patients’ underlying attributes and disease severity or of the care they received. Therefore, this analysis in and of itself does not justify regionalization of ovarian cancer surgery in The Netherlands to specialty centers. Although there are many reasons that explain why the care may be superior in specialty centers, the survival differences are quite modest and there is considerable evidence of selection when it comes to hospital choice. The data presented hint that generalized hospitals in The Netherlands may treat the very old and infi rm, who do not undergo surgery at all, as well as patients with early-stage uncomplicated disease, who generalist gynecologists may be more comfortable managing. Such a heterogeneous mixture of patients would attenuate differences in survival outcomes between generalized and specialized centers. The optimal strategy to mitigate selection bias is randomization. If women could be randomly assigned to receive their care in particular hospitals and systematic differences in their outcomes were evident, then we would have convincing evidence about how to organize care. However, the practical obstacles to randomly