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

Background: The proportion of cases notified by death certificate only (DCO) is a commonly used criterion to judge completeness of cancer registration even though it is affected by additional factors, particularly during initial years of newly established registries.

Methods: Based on cancer registry data from the United States, we provide model calculations to demonstrate the magnitude and time course of the impact of the following mechanisms on DCO proportions of "young" registries: registration of cancer deaths from patients diagnosed prior to the registration period and delayed registration by death certificate of patients diagnosed but not reported after initiation of registration.

Results: DCO proportions of up to ≥30% can be expected from deaths of previously diagnosed patients during the first year of registration. Although this proportion is expected to gradually diminish over subsequent years, DCO proportions may be dominated for several years by this source, which may still be relevant after 10 or more years of cancer registration for cancers with relatively large proportions of late deaths. Otherwise, however, underreporting during patients' lifetime is expected to become the predominant source of DCO proportions in the long run.

Conclusions: Our results may guide interpretation of DCO proportions of relatively "young" cancer registries.