Deriving Valid Population–Based Cancer Survival Estimates in the Presence of Nonnegligible Proportions of Cancers Notified by Death Certificates Only

Abstract

Background: Studies of cancer survival by population-based cancer registries are a key component in monitoring progress against cancer. Patients notified by death certificates only (DCO) are commonly excluded from such studies. The validity of this "exclude DCO" approach has been questioned and an alternative "correct for DCO" approach has been proposed.Methods: We assess the validity of both the "exclude DCO" approach and the "correct for DCO" approach using model calculations. We illustrate implications for population-based cancer survival analyses by analyses of 5-year relative survival of cancer patients in Saarland, Germany.Results: The "exclude DCO" approach provides (too) optimistic survival estimates and the "correct for DCO" approach provides (too) pessimistic survival estimates under plausible assumptions. For example, in case of true survival of 50%, underascertainment of 5% of surviving patients and of 15% of dying patients (yielding a proportion of DCO cases of 7.7%), the two approaches would provide survival rate estimates of 52.8% and 48.8%, respectively. The difference of survival estimates obtained with both approaches increases with incompleteness of registration and the proportion of DCO cases. Trace back of DCO cases shifts survival estimates from the former toward the latter estimate.Conclusions: In case of nonnegligible DCO proportions, cancer survival studies should not be exclusively based on either the "exclude DCO" or the "correct for DCO" approach. A combination of estimates from both approaches may be useful to delineate a plausibility range for true survival.Impact: Our results may help to enhance validity and comparability of population-based cancer survival estimates. Cancer Epidemiol Biomarkers Prev; 20(12); 2480-6. Ó2011 AACR.

Determinants and interpretation of death certificate only proportions in the initial years of newly established cancer registries

“…For example, underreporting was assumed to be independent of covariates related to prognosis, such as age or stage at diagnosis, an assumption that is unlikely to hold in practice. 6 However, the overall temporal patterns of the impact on DCO proportions did not materially change in additional sensitivity analyses allowing for plausible patterns with more severe underreporting during lifetime of cases who died from their cancer than of cases who did not (data not shown).…”

“…[1][2][3][4] A commonly used data quality indicator is the proportion of cases notified by death certificate only (DCO). 2,5,6 Such cases may arise from various sources, including incomplete registration during lifetime of patients dying from cancer. DCO proportions are therefore often used as a criterion for inclusion of cancer registries in collaborative studies on cancer incidence and survival.…”

Breast Cancer Survival in Germany: A Population-Based High Resolution Study from Saarland

“…With ongoing implementation of specialized BRC units [57,58], which started in Saarland in 2004 [59], the database has markedly improved in terms of completeness of information. The proportion of BRC patients with DCO notified tumors was rather small, and the exclusion of these patients from the analyses only had a negligible effect on the derived survival estimates[60]. …”

Population level survival of patients with chronic myelocytic leukemia in Germany compared to the US in the early 21st century

“…Exclusion of these DCO cases in the analysis may lead to some overestimation of survival [37,38]. Exploring the potential magnitude of such overestimation by plausibility ranges [39] suggests that true survival in Germany might be up to a few percentage points lower than estimated. Thus, the survival gap between Germany and the US might be even somewhat larger than suggested by the available data, especially in the older age groups in which DCO proportions are highest.…”