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OPEN ACCESS ARTICLE
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Epidemiology and Community Health |
aDivision of Clinical Epidemiology and Aging Research, German Cancer Research Center, Heidelberg, Germany; bWeill Cornell Medical Center, New York, New York, USA
Key Words. Cancer registries • Hodgkin's lymphoma • Prognosis • Survival
Correspondence: Hermann Brenner, M.D., M.P.H., Division of Clinical Epidemiology and Aging Research, German Cancer Research Center, Bergheimer Str. 20, D-69115 Heidelberg, Germany. Telephone: 49-6221-548140; Fax: 49-6221-548142; e-mail: h.brenner{at}dkfz-heidelberg.de
Received December 22, 2008; accepted for publication June 28, 2009; first published online in THE ONCOLOGIST Express on July 31, 2009.
Disclosures: Hermann Brenner: None; Adam Gondos: None; Dianne Pulte: None.
The content of this article has been reviewed by independent peer reviewers to ensure that it is balanced, objective, and free from commercial bias. No financial relationships relevant to the content of this article have been disclosed by the authors or independent peer reviewers.
| ABSTRACT |
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| INTRODUCTION |
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One major obstacle in deriving truly up-to-date estimates of long-term survival at the population level is the delay in availability of cancer registry data, which is typically in the range of several years, even in the best cancer registries in the world. For example, the most recent cancer registry data from the SEER program are typically available approximately 3 years after the last calendar year included in the database [3]. With further delay in analysis and publication, survival analyses from these data are typically available only
5 years after the last calendar year included. To overcome the delay resulting from availability, analyses, and reporting of cancer registry data, model-based projections of long-term survival have recently been proposed [4]. An empirical evaluation using data from the Finnish Cancer Registry showed this approach to provide up-to-date and accurate data on long-term cancer survival even with the common delay in cancer registration. However, no evaluation or application for patients with HL has been reported to date.
The aim of this study was to derive estimates of long-term survival expectations for patients with HL diagnosed in 2006–2010 using model-based projection, after thorough empirical evaluation of the performance of this method.
| MATERIALS AND METHODS |
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For this analysis, we selected 20,879 patients aged
15 years with a first diagnosis of HL (and no previous cancer diagnosis) between 1973 and 2005, who had been followed for vital status until the end of 2005. After exclusion of 69 patients (0.3%) who were reported by autopsy only and 75 patients (0.4%) who were reported by death certificate only, there remained 20,735 patients (99.3%) for the survival analysis.
Empirical Evaluation of the Projection Approach
In the first step, we empirically evaluated the performance of the model-based projection approach compared with traditional cohort and period analyses to derive up-to-date survival estimates using historical data. The principle of this evaluation is illustrated in Figure 1. First, we calculated the 5-year survival rate actually observed for patients diagnosed in 1996–2000, that is, the most recent cohort of patients for whom a 5-year follow-up was complete by the end of 2005, the closing year of incidence and follow-up in the SEER 1973–2005 database (Fig. 1, upper block). Next, we compared the 5-year survival rate of this cohort with the most up-to-date estimates of the 5-year survival rate that might have been obtained in 1996–2000, that is, at the time of diagnosis of this cohort, by the following methods of survival analysis.
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With period analysis (Fig. 1, third block), an estimate of the 5-year survival rate exclusively reflecting the survival experience of patients in 1991–1995 could have been obtained in 1998, which would have been derived from patients diagnosed in 1986–1995. Period analysis, first introduced by Brenner and Gefeller in 1996 [6], has been shown by extensive empirical evaluation to quite closely predict 5-year survival rates later observed for patients diagnosed in the respective period [7, 8].
With the projection approach (Fig. 1, bottom block), the numbers of deaths and numbers of persons at risk for single years following diagnosis would first have been derived separately for each of the periods 1981–1985, 1986–1990, and 1991–1995. Then, a generalized linear regression model with binomial error structure would have been fitted, with the proportion of survivors among persons at risk as the dependent variable, years following diagnosis as a categorical predictor variable, and grouped years of follow-up (categories: 1981–1985, 1986–1990, and 1990–1995) as a numerical predictor variable. This model estimates a linear trend in the follow-up year–specific survival rates from the periods 1981–1985 to 1991–1995 and can be used to project follow-up year–specific survival in 1996–2000, assuming continuation of this trend. A detailed description of this modeling approach is given elsewhere [4] (the only difference in the approach applied in this analysis is the use of a binomial rather than a Poisson regression model).
We then calculated the difference between the 5-year survival rate estimates obtained with each approach and the 5-year survival rates later observed for patients diagnosed in 1996–2000. Analogous calculations were done for cohorts of patients diagnosed in 1995–1999, 1994–1998, and 1993–1997, that is, all 5-year cohorts of patients for whom such analyses could be carried out with the SEER-9 1973–2005 database. All analyses were carried out for all age groups combined, as well as separately for the following seven age groups: 15–24, 25–34, 35–44, 45–54, 55–64, 65–74, and 75+.
Application of the Modeling Approach to Project Survival in 2006–2010
In the second step, the projection approach was employed to project the 5-year survival rate as well as the 10-year survival rate in 2006–2010. Note that preliminary empirical evaluation of the projection approach for the 10-year survival rate was not possible because it would have required an even longer time series of data than what is available in the SEER-9 1973–2005 database. Again, the most up-to-date estimates of the 5- and 10-year survival rates available from traditional cohort analysis, pertaining to cohorts of patients diagnosed in 1996–2000 (5-year survival rate) or 1991–1995 (10-year survival rate) and period analysis (pertaining to the calendar period 2001–2005), were calculated for comparison.
According to standard practice in population-based cancer survival analysis, relative rather than absolute survival rates were calculated in all analyses. Relative survival rates reflect the survival of cancer patients compared with the survival of the general population [9, 10]. The latter was derived according to the so-called Ederer II method [11] from U.S. sex-, age-, and race-specific life tables [12].
All analyses were performed with the SAS software package, version 9.1 (SAS Institute Inc., Cary, NC) using appropriate adaptations of previously described macros for standard period analysis and model-based projections [4, 13].
| RESULTS |
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Application of the modeling approach to project survival in 2006–2010 yielded 5- and 10-year relative survival rate estimates that were, in most cases, higher than the most-up-to-date survival rate estimates obtained by period analysis (pertaining to the 2001–2005 period) or cohort analysis (pertaining to the cohort of patients diagnosed in 1996–2000 in the case of the 5-year survival rate and to the cohort of patients diagnosed in 1991–1995 in the case of the 10-year survival rate) (Table 3). Overall, differences were more pronounced for the 10-year relative survival rate (82.6% versus 80.4% and 76.3%) than for the 5-year relative survival rate (86.7% versus 85.2% and 84.6%). According to the projection, the 10-year relative survival expectations of patients diagnosed in 2006–2010 are close to or exceed 90% in all age groups up to 45 years of age, and still exceed 80% and 70% in the 45–54 and 55–64 age groups, respectively. In most cases, the most up-to-date estimates available from traditional cohort analysis and period analysis are lower, with differences ranging up to –11.1 and –6.6 percentage points for the cohort analysis and period analysis, respectively. Patterns seemed to be different in the oldest age group, but need to be interpreted with caution, given the large standard errors for the survival estimates in that group.
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| DISCUSSION |
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65 years, the 10-year relative survival expectations remain much lower, at levels <50%. The survival rates of patients with a diagnosis of HL in 2006–2010 projected in this study are substantially higher than previously available survival estimates, many of which still refer to patients diagnosed and treated in the 1990s [14, 15]. They are also higher than the few available period estimates for the beginning of the 21st century from a previous analysis from our group and a recent report from the EUROCARE-4 study [2, 16]. For example, using a period analysis for the years 2000–2002, the 5-year relative survival rate for all ages combined was 81.4% in European countries. The 5-year relative survival rate in the SEER-13 database for the same time period was calculated as 80.6%, and no estimates of the 10-year relative survival rate were provided [16].
Clearly, the validity of our projections depends on whether and to what degree the implicit assumption holds that the previously observed steady upward trend in survival has continued in the most recent years. Given the steady improvement seen in previous decades, the projection method showed excellent performance in the empirical evaluation, and, with two exceptions, consistently provided more up-to-date and more valid estimates of long-term survival than traditional cohort analysis and also standard period analysis [6, 13]. The only major failure of the projection occurred in one of the analyses for the oldest age group, possibly because of random variation, given the large standard errors of the survival estimates in this comparably small group.
Within previous decades, improvements in radiation therapy, chemotherapy, and stem cell transplantation have been the driving forces behind the improvement in survival. Over the past several decades, the use of combination chemotherapy and improvements in this therapy have contributed greatly to increasing survival rates for patients with HL [17, 18]. Additionally, the use of high-dose salvage chemotherapy and hematopoietic stem cell transplantation in relapse has contributed to improvements in survival [19]. Survival has continued to rise since the 1990s, even though there has been only incremental therapeutic improvement and there has been a shift in focus from the implementation of even more effective therapy to the implementation of equally effective, but less toxic, therapy, such as the use of smaller radiation fields, which have been demonstrated to reduce toxicity without reducing treatment efficacy [20]. A possible explanation for the ongoing increase in survival in population-based analyses despite limited therapeutic improvement could be the more widespread use of effective therapy. In particular, the observed catch-up of older patients with respect to survival expectations may reflect both the increased use and less toxicity of new therapeutic regimens among older patients, and increased use of high-dose therapy and hematopoietic stem cell transplant in patients into the 6th and 7th decades of life. In addition, more refined diagnostic techniques, especially in older age groups, and better staging techniques may also have contributed to longer survival. Given the very high levels of survival currently achieved in younger patients, with a 10-year relative survival rate
90%, less room is left for any further increase in survival in these age groups, and limiting adverse sequelae of therapy in terms of quality of life, second malignancies, and comorbidity may even become more important. Among older patients, however, despite the recent catch-up, there remains a large potential for coming closer to the very high survival rates currently observed for younger patients.
In the interpretation of our data, a number of limitations have to be kept in mind. Given the limited data on therapy included in the SEER database, direct assessment of the impact of changes in therapy on survival is not possible. Even the long time series of data included in the SEER database, currently 1973–2005, was insufficient to carry out empirical evaluation of projections of the 10-year survival rate in the same way as was done for the 5-year survival rate. There is no obvious reason why the method should be less useful for the 10-year survival rate than for the 5-year survival rate. However, as previously shown for estimates of the 10-year survival rate obtained by standard period analysis [7, 8], the projections of the 10-year survival rate (obtained by extrapolation of trends in period estimates) are still expected to be somewhat too pessimistic in cases of ongoing improvements in survival. Finally, keeping long-term morbidity and mortality from second cancers and other potential late effects of therapy in mind, extension of the projections to longer-term survival estimates, such as 15-, 20-, or 25-year survival rates, is desirable, but would require even longer time series of population-based cancer registry data.
| CONCLUSIONS |
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| AUTHOR CONTRIBUTIONS |
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Data analysis: Hermann Brenner, Adam Gondos, Dianne Pulte
Manuscript writing: Hermann Brenner
Final approval of manuscript: Hermann Brenner, Adam Gondos, Dianne Pulte
| ACKNOWLEDGMENT |
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| REFERENCES |
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This article has been cited by other articles:
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