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Background: The proportion of cases notified by death certificate only (DCO) is a commonly used data quality indicator in studies comparing cancer survival across regions and over time. We aimed to assess dependence of DCO proportions on the age structure of cancer patients. Methods: Using data from a national cancer survival study in Germany, we determined age specific and overall (crude) DCO proportions for 24 common forms of cancer. We then derived overall (crude) DCO proportions expected in case of shifts of the age distribution of the cancer populations by 5 and 10 years, respectively, assuming age specific DCO proportions to remain constant. Results: Median DCO proportions across the 24 cancers were 2.4, 3.7, 5.5, 8.5 and 23.9% in age groups 15-44, 45-54, 55-64, 65-74, and 75+, respectively. A decrease of ages by 5 and 10 years resulted in decreases of cancer specific crude DCO proportions ranging from 0.4 to 4.8 and from 0.7 to 8.6 percent units, respectively. Conversely, an increase of ages by 5 and 10 years led to increases of cancer specific crude DCO proportions ranging from 0.8 to 4.8 and from 1.8 to 9.6 percent units, respectively. These changes were of similar magnitude (but in opposite direction) as changes in crude 5-year relative survival resulting from the same shifts in age distribution. Conclusions: The age structure of cancer patient populations has a substantial impact on DCO proportions. DCO proportions should therefore be age adjusted in comparative studies on cancer survival across regions and over time. [ABSTRACT FROM AUTHOR]

Abstract: The measures of cancer prognosis most commonly reported by cancer registries are 5- or 10-year absolute or relative survival rates. Because cancer survival rates often vary by the age of cancer patients, and because the age structure of cancer patients often varies between populations, age adjustment is crucial for comparative analyses of cancer survival rates. However, traditional age adjustment often breaks down for long-term survival rates, particularly for sparse data, and it may provide inconsistent results for relative survival rates, even if age adjustment is made to the study population’s own age distribution. In this manuscript, we propose an alternative approach to age adjustment of both absolute and relative survival rates to overcome both the practical and conceptual problems inherent in traditional age adjustment. We outline the computational realisation of this approach, and we give an empirical illustration of its application using data from the nationwide Finnish Cancer Registry. [Copyright &y& Elsevier]

Relative survival rates, such as 5- or 10-year relative survival rates, which quantify “net survival” of cancer patients, are the most commonly reported measures of cancer outcome by cancer registries. Because relative survival rates vary with age for many forms of cancer, and because the age distribution of cancer patients varies between different populations or within one population over time, age adjustment of relative survival rates is often employed in international comparisons or in time series analyses of cancer patient survival. In this article, we show that derivation of crude and of age-adjusted relative survival rates in the traditional way is conceptually inconsistent, and that this inconsistency has important practical implications. We show ways to overcome this inconsistency in the derivation and interpretation of crude and age-adjusted relative survival rates. [Copyright &y& Elsevier]