EU Biosimilar Approval Requirements: Comparability Exercises, Clinical Data, and Tailored Development Programs

Biosimilar approval in the EU: comparability, clinical data, and the shift to tailored development

The EU created the world's first dedicated biosimilar framework, and the regulatory logic behind it has stayed constant while the evidentiary burden has steadily shifted. A biosimilar is not approved by re-proving clinical benefit. It is approved by demonstrating that it is highly similar to an already-authorised reference biological, so that the reference product's established safety and efficacy can be relied upon ¹²²⁵. Everything else in an EMA biosimilar dossier follows from that single objective, and the most important recent development is that CHMP has now formally endorsed reducing the clinical portion of the exercise when the analytical case is strong enough.

The core principle: comparability, not independent proof of benefit

EMA requires the developer to establish similarity to the reference medicinal product "by the best possible means," so that the previously proven safety and efficacy of the reference product also apply to the biosimilar ¹²²⁵. The biosimilar must be highly similar in physicochemical and biological terms, and any differences observed must be justified for their potential impact on safety and efficacy ¹²²⁵. If the comparability exercise reveals relevant differences that make biosimilarity unlikely, the applicant is expected to abandon the biosimilar route and consider a stand-alone development instead ¹²²⁵¹¹⁹.

The demonstration rests on the totality of evidence. The conclusion on biosimilarity is based on the combined quality, biological, non-clinical, pharmacokinetic (PK), pharmacodynamic (PD), efficacy, safety and immunogenicity data taken together, not on any single study in isolation ³²³⁸⁵⁶⁵². The stated aim across the entire package is to exclude any relevant differences between the biosimilar and the reference product, using methods and studies sensitive enough to detect such differences if they exist ¹²²⁵.

The stepwise comparability exercise

EMA structures development as a stepwise process that begins with analytics and adds clinical work only to the extent that residual uncertainty requires it ¹²²⁵.

Development normally starts with comprehensive physicochemical and biological characterisation ¹²²⁵.
The extent of subsequent non-clinical in vivo and clinical studies depends on the evidence generated earlier, including the robustness of the analytical and in vitro data ¹²²⁵.
Clinical data are used to address slight differences seen at earlier steps and to confirm comparable clinical performance. Clinical data cannot be used to justify substantial quality differences ²⁵.
The clinical programme itself is stepwise, beginning with PK and, where feasible, PD studies, followed by efficacy and safety studies, or in some cases confirmatory PK/PD studies instead of an efficacy trial ⁴⁷⁵².

This ordering matters for strategy: the quality package is the foundation that determines how much clinical work a programme actually needs.

The quality (analytical) comparability exercise

The analytical comparison is the most demanding part of the dossier. EMA expects an extensive, side-by-side quality comparability exercise using state-of-the-art, appropriately qualified analytical methods sensitive enough to detect slight differences between the two products ²³²⁴²⁹⁴⁰. The applicant must demonstrate that the chosen methods can detect slight differences in all aspects pertinent to quality ²²²³²⁹.

Structural and physicochemical characterisation should cover composition, physical properties, and primary and higher-order structure, and should identify product-related substances and impurities ²²²³. In practice this includes:

confirming the target amino acid sequence, which is expected to be the same as the reference product ²²²³;
comparing N- and C-terminal sequences, free SH groups, and disulfide bridges as appropriate ²²²³;
quantifying modifications and truncations and describing intrinsic or expression-system-related variability ²²²³;
characterising post-translational modifications, including the overall glycan profile, site-specific glycosylation, and site occupancy ²²²³;
justifying any differences against the micro-heterogeneity pattern of the reference product ²³.

Functional and biological characterisation is treated as an essential element of the profile, using different and complementary (orthogonal) assay approaches such as ligand or receptor binding assays, enzymatic assays, cell-based assays, and other functional assays ²²²⁷. Bioassays should be sensitive, specific and sufficiently discriminatory to detect changes in biological activity, and results should be expressed in calibrated activity units where possible ²²²⁷. Where direct side-by-side testing is not feasible, sample handling should be outlined, validated, and its impact documented and discussed ²²²³²⁹. Pharmacopoeial or WHO reference standards should be used where applicable ²²²³²⁹.

Non-clinical data: in vitro is now paramount

EMA's position is that in vitro pharmaco-toxicological studies carry the weight of the non-clinical comparison, and the need for any in vivo study should be thoroughly scrutinised. The recommended approach is to run analytical and in vitro studies first, then decide what, if any, in vivo work is needed ⁶⁴. EMA has explicitly described the value of in vivo data in the biosimilarity assessment as limited, with in vivo studies generally not needed and analytical and in vitro data taking priority ⁶⁹. The non-clinical guideline frames the approach as one to be tailored to the product on a case-by-case basis and fully justified, with in vitro studies treated as paramount ⁶⁵.

Clinical data expectations

The clinical package confirms comparable clinical performance rather than re-establishing patient benefit ⁴⁸⁴⁹⁹⁶³. Its extent is driven by the uncertainty left after the analytical and functional work.

PK studies are an essential part of biosimilar development ⁵³. They compare the biosimilar and reference product for key PK parameters and must be designed for the clinical context, PK characteristics, half-life and immunogenicity risk of the molecule ⁵³⁵⁵. EMA favours the most sensitive model, often healthy volunteers where appropriate, and a single-dose crossover design for many products, with a parallel-group design where a long half-life or high immunogenicity makes crossover impractical ⁵³⁵⁵. Typical parameters include AUC, Cmax, and half-life or clearance, with Ctrough or truncated AUC in some multiple-dose settings ⁵³⁵⁵⁴³. Anti-drug antibodies are measured in parallel with PK ⁵⁷. Equivalence margins for the main PK parameters must be defined a priori and justified ⁵³⁵⁵⁵⁸⁴³.

PD studies should be added to PK studies whenever feasible, with markers chosen for their relevance to clinical outcome ⁵⁷. Comparative PK/PD studies can be sufficient to demonstrate clinical comparability where the PD marker is an accepted surrogate linked to patient outcome, or where there is a clear dose- or concentration-response relationship and the study is performed in the sensitive part of that curve ⁵⁷. For monoclonal antibodies, PD-based pivotal evidence may be possible if the markers are clinically relevant and safety and immunogenicity are adequately addressed ⁴⁹.

Comparative efficacy trials. Where a suitable surrogate PD marker is not available, an efficacy trial is usually necessary ⁵⁷⁶³. EMA normally expects an adequately powered, randomised, parallel-group, preferably double-blind comparative trial, and normally an equivalence design ⁴⁴⁸⁴⁹⁹⁵⁸⁶³. The trial should use a homogeneous and sensitive patient population and the most sensitive endpoint and model available so that it can detect product differences if they exist ⁴⁴⁸⁹. Equivalence margins must be pre-specified and justified on both statistical and clinical grounds using reference-product data ⁴⁸⁴⁹⁵³⁵⁵⁵⁸⁴³.

When a confirmatory efficacy trial may be waived. EMA guidance already allows exceptions. A confirmatory efficacy trial may not be needed where physicochemical, structural and in vitro biological analyses, combined with human PK and supportive PD marker data, provide robust evidence of comparability ⁵⁷. Conversely, a trial is still needed where dose-comparative and highly sensitive PD studies cannot convincingly show comparability, or where no suitable surrogate marker for efficacy exists ⁵⁷⁶³. This case-by-case exception is the seed of the broader tailored approach described below.

Safety and immunogenicity. Clinical safety is captured during PK/PD evaluation and the pivotal comparability study, with immunogenicity requiring particular attention ⁷⁵²⁵⁶⁹. Actively controlled safety data should normally be collected pre-authorisation, and the follow-up duration should be justified ⁷. Where PD studies serve as the pivotal evidence, the applicant must still provide sufficient reassurance of comparable clinical safety, especially immunogenicity ⁴⁷⁹⁵⁷.

Comparative immunogenicity

Comparative immunogenicity assessment is always required in biosimilar development ¹³. It is conducted within the comparability exercise, using the same assay format and sampling schedule for both products, tested in parallel and preferably blinded ¹²³⁸. Assays should preferably detect antibodies against both the biosimilar and the reference molecule, and at minimum must detect all antibodies against the biosimilar ³⁸. The assay strategy must be validated and cross-validated using both antigens, antibody-positive controls and preferably clinical samples ¹. The assessment should measure and present the incidence, nature and titres of antibodies, including cross-reactivity, target epitopes and neutralising activity, and interpret these against possible effects on efficacy and safety ³⁸. Higher immunogenicity of the biosimilar versus the reference may call biosimilarity into question, whereas lower immunogenicity does not preclude approval ¹²⁸. For chronic treatment, one year of pre-authorisation follow-up is normally required unless a shorter period is justified ²⁸.

Extrapolation of indications

Once biosimilarity is established and supported by the totality of evidence, EMA permits extrapolation from a studied indication to other indications held by the reference product, provided the extrapolation is scientifically justified ⁹²⁹³¹⁰⁴⁴. The justification should address:

whether the mechanism of action and the relevant receptors or binding sites are the same across studied and non-studied indications ⁹²⁹³⁹⁵⁹⁶¹¹¹;
whether any indication involves a different or uncertain mechanism of action, which may require additional data ⁹²⁹³⁹⁵⁹⁶;
whether the studied indication is sensitive enough to detect differences relevant to the other indications ⁹³⁹⁵;
immunogenicity, which can differ by indication and route of administration and therefore needs specific justification if extrapolated ⁹²⁹³⁹⁴⁹⁵;
a comprehensive discussion of the literature and the antigen, receptors and mechanisms involved ⁹²⁹⁶.

For more challenging cases, EMA expects an extensive quality and non-clinical database, including potency and in vitro functional assays, supplemented by relevant clinical data ⁹²⁹⁶. CHMP comments on biosimilar monoclonal antibodies stress that extrapolation should be tailored to the reference product's benefit and customised for each indication, particularly where cure is the expected outcome ⁷⁴⁷⁷.

The move toward tailored development programmes

The direction of travel is unambiguous: more reliance on analytical and PK data, less mandatory in vivo and clinical testing, with the clinical package sized to the specific product. Importantly, EMA and CHMP frame this as tailoring, not lowering standards. CHMP/BMWP comments state that biosimilar guidance is meant to help applicants design a tailored development programme, not an abbreviated one, and is "not about minimal or low standards" but about adequate and sufficient requirements to safeguard safety and establish biosimilarity ⁷⁰⁷¹⁷³.

The regulatory milestones:

2012 to 2013: EMA revised the overarching biosimilar guidelines, beginning with the quality guideline in 2012 ⁷⁶. The 2013 non-clinical guideline established that the approach "may be considered and should be tailored to the product concerned on a case-by-case basis," with in vitro studies treated as paramount ⁶⁵.
2018: CHMP adopted technical updates to certain biosimilar guidelines to reflect best practice in 3Rs implementation, rather than full revisions ⁹¹.
2021: CHMP ran a pilot of tailored biosimilar scientific advice for developers who presented extensive quality and in vitro non-clinical data pointing toward a tailored further development path ⁸⁷.
2024: EMA published a concept paper setting out a tailored clinical approach in biosimilar development, which later work builds upon ⁴⁵⁴⁴.
April 2025: EMA published a draft reflection paper on streamlining biosimilar development and assessment, stating that the approach could reduce the amount of clinical data required for development and approval and potentially waive certain clinical data requirements while maintaining safety and efficacy standards. Stakeholders were invited to comment by 30 September 2025 ⁴⁵. In parallel, EMA has been drafting an overarching reflection paper intended to replace most product-specific biosimilar guidelines, reflecting the accumulated experience that in vivo studies have limited value in the comparability exercise ⁶⁴⁶⁹.
March 2026: CHMP adopted a reflection paper on a tailored clinical approach in biosimilar development, with the explicit aim of reducing the amount of clinical data required for the development and approval of certain biosimilar medicines in the EU ⁴⁶.

What the tailored approach means in practice is authorisation based on comparability demonstrated at the quality level, supported by a limited clinical data package rather than a full comparative efficacy trial ⁴⁴. This extends, as general policy, the exception EMA guidance already recognised for individual products: where analytical, functional and PK evidence is robust, a confirmatory efficacy study may not add meaningful information ⁵⁷. The reflection papers do not remove the clinical comparability concept. Comparative PK, and where relevant PD, immunogenicity and safety data remain part of the package ⁴⁴, and comparative immunogenicity in particular is still always required ¹³.

Practical takeaways for developers

The analytical and functional comparability package is now the decisive part of an EU biosimilar dossier, because it determines how much clinical work a programme needs ¹²²⁵⁶⁴. Comparative PK studies with pre-specified, justified equivalence margins remain a fixed requirement ⁵³⁵⁵⁵⁸. A comparative efficacy trial is the default only where PD-based comparability cannot be convincingly demonstrated ⁵⁷⁶³, and CHMP's March 2026 reflection paper signals that, for suitable products, this default is being relaxed toward a limited clinical package anchored on quality and PK data ⁴⁶⁴⁴. Developers weighing an EU strategy under the new framework should use EMA scientific advice, including tailored biosimilar advice, early, since the acceptability of a reduced clinical package is decided case by case on the strength of the analytical evidence ⁸⁷⁵⁷.