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Term of the Day

Natural history study

A natural history study is a preplanned observational study intended to track the course of a disease over time, identifying demographic, genetic, environmental and other variables that correlate with its development and outcomes in the absence of intervention, or under standard of care. Designs may be retrospective (chart review of existing records) or prospective (longitudinal follow-up of a cohort or registry).

Natural history data is particularly important in rare and paediatric diseases, where randomised placebo-controlled trials may be infeasible or unethical. The FDA (guidance on rare disease natural history studies, 2019) and the EMA accept well-designed natural history studies to define endpoints and biomarkers, identify patient subgroups, estimate sample sizes and, in some cases, serve as external or historical control arms for single-arm trials supporting orphan products.

Because they are non-interventional, natural history studies fall outside the CTR and are governed by national law (for example France's MR-003 or MR-004 reference methodologies) and by the GDPR. They typically involve secondary use of medical records, long-term follow-up, genetic data and small populations in which anonymisation is rarely achievable, so pseudonymisation, a DPIA and a robust research legal basis under Art. 9(2)(j) are essential. Registries maintained by patient organisations or academic consortia raise additional questions of joint controllership and data access governance.

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Legitimate interest

Legitimate interest is the legal basis in Art. 6(1)(f) GDPR under which processing is lawful if it is necessary for the purposes of the legitimate interests pursued by the controller or by a third party, except where such interests are overridden by the interests or fundamental rights and freedoms of the data subject, in particular where the data subject is a child. It is the most flexible of the six legal bases and the only one that requires the controller to weigh its own interests against those of individuals.

The EDPB Guidelines 1/2024 and the Court of Justice (Rīgas satiksme, C-13/16; Meta Platforms, C-252/21; KNLTB, C-621/22) set a three-step test: the interest must be legitimate (lawful, clearly articulated, real and present, and it may be commercial); the processing must be necessary, meaning no less intrusive means would achieve it; and the balancing must come out in favour of the controller, taking into account the reasonable expectations of data subjects, the nature and sensitivity of the data, the consequences of processing and the safeguards applied. The controller must document this in a legitimate interest assessment, name the interests pursued in its information notice (Art. 13(1)(d)), and honour the right to object under Art. 21. Public authorities cannot rely on it in the performance of their tasks, and legitimate interest alone never lifts the Art. 9 prohibition for special category data, which needs an additional exception such as Art. 9(2)(j).

In life sciences, legitimate interest is commonly used by private sponsors for clinical trial conduct (combined with Art. 9(2)(j) research) where public interest is unavailable to private bodies under national law, for secondary research on existing data, for processing of investigator and healthcare professional data, for fraud prevention and IT security, and for B2B marketing. It is not suitable where the imbalance of power is stark, where data subjects would not expect the processing, or where national law prescribes another basis, as French reference methodologies do. The UK Data (Use and Access) Act 2025 added a list of "recognised legitimate interests" that dispense with the balancing test for defined purposes.