Death certificates are an important source of information for cancer registries. The aim of this study was to validate the cancer information on death certificates, and to investigate the effect of including death certificate initiated (DCI) cases in the Cancer Registry of Norway when estimating cancer incidence and survival.
All deaths in Norway in the period 2011–2015 with cancer mentioned on the death certificates were linked to the cancer registry. Notifications not registered from other sources were labelled death certificate notifications (DCNs), and considered as either cancer or not, based on available information in the registry or from trace-back to another source.
From the total of 65 091 cancers mentioned on death certificates in the period 2011–2015, 58,425 (89.8%) were already in the registry. Of the remaining 6 666 notifications, 2 636 (2 129 with cancer as underlying cause) were not regarded to be new cancers, which constitutes 4.0% of all cancers mentioned on death certificates and 39.5% of the DCNs. Inclusion of the DCI cases increased the incidence of all cancers combined by 2.6%, with largest differences for cancers with poorer prognosis and for older age groups. Without validation, including the 2 129 disregarded death certificates would over-estimate the incidence by 1.3%. Including DCI cases decreased the five-year relative survival estimate for all cancer sites combined with 0.5% points.
In this study, almost 40% of the DCNs were regarded not to be a new cancer case, indicating unreliability of death certificate information for cancers that are not already registered from other sources. The majority of the DCNs where, however, registered as new cases that would have been missed without death certificates. Both including and excluding the DCI cases will potentially bias the survival estimates, but in different directions. This biases were shown to be small in the Cancer Registry of Norway.
A large proportion of death certificate notifications not a new cancer case.
Death certificate initiated cases increase incidence but bias survival downwards.
Excluding death certificate initiated cases will bias survival upwards.
Only minor survival bias in the Cancer Registry of Norway.
Death certificates with underlying and contributing causes of death are an important source of information for cancer registries. Lack of such information has impact on both incidence and survival. Incidence will be lower if death certificates are not included as a source, especially for sites with poorer prognosis like pancreatic and lung cancer. For survival, not to include death certificates as a source for cancer registration can lead to survival estimates that are too high , as cases with poor prognosis and correspondingly short survival are potentially more likely to be missed by other sources .
Cancer cases that rely on death certificates to be registered are called Death Certificate Initiated (DCI) cases. If no further information is received after trace-back, the case is labelled Death Certificate Only (DCO). Most cancer registries world-wide publish the proportion of DCO cases, and this is included in the IARC-report Cancer Incidence in Five Continents, as an indicator of data quality . The proportion of DCI cases is an indicator of completeness, but is usually not published in summary reports from cancer registries. Andersson and co-workers emphasized the importance of DCI cases and recommend that population-based cancer registries report this measure .
The accuracy of the information on the death certificates have, however, long been called into question . Taking the specific cancer diagnosis from the death certificate at face value without validation against other sources and a trace-back routine in place could thus both lead to erroneous registrations of cases and render a larger proportion of the DCI cases to remain DCOs.
In this study, we aim to 1) validate the cancer information on death certificates based on information available in the Cancer Registry of Norway and 2) show the impact of including DCI cases when estimating incidence and survival. We will not validate if the person dies from cancer or not, only whether or not the specific cancer information on the death certificate is trustworthy.