Background
Population-based cancer registries (PBCRs) provide systematic and standardised information on cancer incidence, forming the basis for cancer surveillance. These data underpin international comparisons and global cancer estimates promoted by the International Agency for Research on Cancer (IARC), as well as the planning of cancer control strategies and public policy evaluation. In Europe, PBCRs operate within heterogeneous legal, organisational and operational contexts, which condition access to data sources, data completeness and comparability. The European Health Data Space (EHDS) introduces a new framework for the secondary use of health data, with the right to opt out as a central element. Its potential effects on core dimensions of data quality (accuracy, completeness, timeliness and comparability) and on different forms of bias, including demographic and socio-economic bias, require explicit consideration, as they may directly affect the validity of cancer surveillance and public health decision-making.
Objective
To analyse the implications of the right to opt out established under the EHDS for the secondary use of PBCR data in Europe, focusing on its potential impact on data quality, representativeness and comparability in public health decision-making.
Methods
A conceptual analysis of the EHDS Regulation was conducted, focusing on provisions related to the right to opt out in the secondary use of health data. This was complemented by a documentary review of secondary sources (ENCR, ECIS and relevant scientific literature) to characterise heterogeneity among PBCRs in Europe in terms of legal and operational mandatory reporting. Based on this information, an analytical typology of PBCRs was developed and used as a framework to examine how national implementation of the right to opt out may introduce additional variability in data availability and governance, without empirical analyses or individual-level databases.
Results
PBCRs in Europe are characterised by pre-existing structural heterogeneity, stemming from differences in legal and operational frameworks governing mandatory cancer reporting and access to data sources. This heterogeneity results in varying degrees of under-ascertainment, with implications for data completeness, representativeness and comparability in population-based incidence and trend analyses.
The introduction of the right to opt out under the EHDS represents an additional and conceptually distinct source of missing data. Unlike structural under-ascertainment, opt-out decisions operate at the individual level and may be non-randomly distributed across population groups, thereby further affecting completeness and the internal validity of incidence estimates and trend analyses. Moreover, differing national approaches to opt-out implementation may add a further layer of fragmentation in the reuse of cancer registry data at the European level.
Conclusions/Implications for practice policy
The right to opt out established under the EHDS poses significant challenges for PBCRs. Its implementation requires a careful balance between the protection of individual rights and the needs of public health surveillance, which rely on the availability of high-quality, representative and comparable data. Explicit recognition of the role and specific characteristics of PBCRs within EHDS governance frameworks is essential to ensure that the exercise of the opt-out right does not undermine the utility of cancer data for evidence-based cancer prevention and control policies.