Integrating Companion Diagnostics into Precision Oncology Trials

What Are Companion Diagnostics and Why They Matter

Companion diagnostics (CDx) are in vitro diagnostic devices or imaging tools essential for the safe and effective use of a corresponding therapeutic product. In oncology, CDx testing is often the gateway to trial enrollment—patients must meet specific biomarker-defined eligibility criteria before receiving the investigational drug. For example, a HER2-targeted therapy requires HER2 amplification confirmation, an EGFR inhibitor needs exon 19 deletions or L858R mutations, and an ALK inhibitor demands ALK rearrangement detection.

The role of CDx is not only to identify patients most likely to benefit but also to exclude those at higher risk of adverse effects. Regulators like the FDA and EMA mandate that, when biomarker-based eligibility is critical, the diagnostic must be validated to the same standard of evidence as the drug itself. This concept is central to precision oncology: the therapy’s approval can be contingent on having an approved CDx available.

Real-world example: Trastuzumab deruxtecan was approved alongside a specific HER2 testing method with defined scoring cutoffs. Without an approved HER2 IHC or ISH assay, trial enrollment would not have been possible. Similarly, osimertinib’s label specifies that only EGFR T790M-positive patients by an FDA-approved test are eligible post-EGFR-TKI resistance.

Regulatory Expectations: FDA, EMA, and Global Considerations

From a regulatory standpoint, companion diagnostics are considered high-risk (Class III in the US, Class C under IVDR in the EU) because incorrect results can lead to inappropriate treatment. The FDA’s guidance “In Vitro Companion Diagnostic Devices” specifies that CDx must demonstrate both analytical and clinical validation. Analytical validation ensures that the assay reliably and reproducibly measures the biomarker; clinical validation confirms the biomarker’s predictive value in identifying patients who will benefit from the therapy.

In the EU, under the IVDR (Regulation (EU) 2017/746), companion diagnostics must be assessed by a notified body and involve consultation with a competent medicines authority, such as the EMA. This adds complexity and timelines, especially for global oncology trials seeking simultaneous approval in multiple jurisdictions. Countries like Japan, China, and Australia have their own specific regulatory frameworks, and harmonizing CDx approvals can be a major operational challenge.

One frequent pitfall in global trials is assuming that a US-approved CDx automatically meets EU or APAC requirements—it often does not. This requires early regulatory strategy alignment between drug and diagnostic development teams, ideally before pivotal trial protocol finalization.

Analytical Validation: Establishing Assay Performance (LOD, LOQ, and More)

Analytical validation parameters for CDx include sensitivity, specificity, limit of detection (LOD), limit of quantitation (LOQ), reproducibility, and robustness. For example, a ctDNA-based assay for detecting EGFR T790M may need an LOD of 0.2% variant allele frequency (VAF) with ≥95% confidence to ensure that eligible patients are not missed. LOQ might be set at 0.5% VAF to ensure reliable quantitation for therapy decision-making.

For cross-contamination risk in diagnostic reagent preparation, applying pharmaceutical cleaning validation concepts like MACO (Maximum Allowable Carryover) and PDE (Permitted Daily Exposure) ensures that no assay-to-assay contamination occurs in multi-test platforms.

Designing Clinical Trials with Companion Diagnostics

When integrating CDx into oncology trials, trial design must reflect the biomarker’s prevalence, predictive power, and the assay’s availability. In an enrichment design, only biomarker-positive patients are enrolled, maximizing effect size but potentially slowing accrual if prevalence is low. An all-comers design with biomarker-stratified analysis allows exploratory evaluation of biomarker-negative patients.

Adaptive designs can allow for mid-trial modifications based on interim biomarker prevalence data, while basket and umbrella trials can leverage a single assay to assign patients to multiple targeted therapies. For example, a comprehensive NGS panel could identify HER2 amplification, BRAF mutations, and RET fusions for allocation to different arms within the same master protocol.

Operationalizing CDx Testing in Trials

Operational success depends on fast turnaround times (TAT) and consistent assay performance across global sites. Establishing a central testing laboratory can standardize results but may increase logistical complexity for sample shipment. Alternatively, a decentralized model with harmonized local labs requires rigorous cross-validation (≥90% concordance with central lab results).

Consent forms must explicitly mention the use of a companion diagnostic, potential incidental findings (e.g., germline BRCA mutations), and data sharing for regulatory purposes. Clinical trial management systems should track test performance metrics, including invalid rates, re-testing frequency, and median TAT.

Reference operational SOPs, such as those available on PharmaGMP.in, to streamline documentation for audits and inspections.

Regulatory Submission and Approval Pathways

The drug and the CDx are often submitted concurrently in a coordinated regulatory package. The FDA requires a premarket approval (PMA) for most CDx devices, while the EMA mandates a CE marking under IVDR rules. Bridging studies may be required if the pivotal trial assay differs from the commercial version, with statistical comparability set at ≥90% concordance.

Post-approval, CDx manufacturers may need to expand the assay’s indications, such as adding ctDNA detection to a tissue-based test. These modifications typically require supplemental PMA submissions or revised technical documentation under IVDR.

Conclusion: Making CDx Work for Precision Oncology

Effective companion diagnostics require early and integrated planning between drug and diagnostic development teams. By aligning regulatory strategies, ensuring rigorous analytical validation, and building operational workflows that can deliver results rapidly and reproducibly, CDx can significantly increase the probability of trial success and regulatory approval. The reward is a therapy that reaches the right patients faster, with robust evidence that the biomarker truly guides treatment benefit.

Strategies for Co-Development of Therapeutics and Companion Diagnostics

The Evolution of Co-Development in Precision Medicine

Precision medicine aims to deliver the right treatment to the right patient at the right time. This goal has fueled the rise of companion diagnostics (CDx), which are laboratory tests or in vitro diagnostics (IVDs) used to identify patients who are likely to benefit from a specific therapeutic product. To meet regulatory expectations and ensure market access, the co-development of drugs and companion diagnostics is now the gold standard.

According to the FDA’s guidance, co-development involves simultaneous clinical and regulatory development of both the drug and the diagnostic test. The European Medicines Agency (EMA) also supports this approach through its integration of the In Vitro Diagnostic Regulation (IVDR) into the centralized drug approval process. This article outlines the key steps, challenges, and best practices for successful co-development.

Why Co-Development Matters

Launching a therapeutic without an approved CDx limits its market reach, delays treatment for eligible patients, and risks non-compliance with global regulations. Co-development ensures that both products are ready for simultaneous approval, which is particularly important for targeted oncology, rare diseases, and immunotherapies.

Benefits of co-development:

• Optimized patient selection during trials
• Stronger clinical evidence for biomarker utility
• Aligned regulatory review timelines (NDA/BLA and PMA)
• Reduced time to market

Example: HER2 testing and trastuzumab (Herceptin) were co-developed, setting the regulatory precedent for modern CDx programs.

Co-Development Workflow and Milestones

Effective co-development requires strategic alignment between drug sponsors and diagnostic partners across development phases. Below is a simplified timeline:

Co-development depends on early assay design decisions, such as the sample matrix (e.g., FFPE, blood), detection method (e.g., NGS, IHC), and anticipated regulatory classification.

Collaborative Models and Legal Agreements

Drug and diagnostic co-development typically involves separate companies. As such, collaborative models must be clearly defined, often through:

• Joint Development Agreements (JDAs)
• Clinical Trial Agreements (CTAs)
• Data sharing protocols
• IP ownership and licensing terms

Successful collaborations clarify roles in assay design, validation, regulatory filing, post-marketing surveillance, and commercial distribution.

Clinical Trial Considerations in Co-Development

When co-developing a drug and CDx, the diagnostic assay must be integrated into the pivotal clinical trial. Key trial design elements include:

• Enrichment or stratified design based on biomarker status
• Assay lock prior to trial initiation
• Validated sample collection and processing SOPs
• Concordance studies if changing assay format between phases

For example, a PD-L1 assay used in an immuno-oncology trial must demonstrate consistent expression quantification and predictive performance before it can be relied upon for regulatory decisions.

Regulatory Requirements: FDA and EMA

The FDA classifies CDx as Class III devices requiring Premarket Approval (PMA), submitted concurrently with the New Drug Application (NDA) or Biologics License Application (BLA). Sponsors must coordinate closely with the Center for Devices and Radiological Health (CDRH) and Center for Drug Evaluation and Research (CDER).

• FDA Requirements:
• Investigational Device Exemption (IDE) for using CDx in trials
• PMA with analytical and clinical validation data
• Labeling alignment between drug and diagnostic

The EMA oversees CDx under the In Vitro Diagnostic Regulation (IVDR). A notified body assesses the diagnostic while EMA evaluates the drug. Coordination is facilitated through joint scientific advice.

Bridging Studies and Analytical Equivalence

If the assay used in the clinical trial differs from the final commercial version, a bridging study is required to demonstrate equivalence. Parameters assessed include:

• Sensitivity and specificity
• Cut-off concordance
• Lot-to-lot variability
• Inter-lab reproducibility

These studies ensure that patients tested with the marketed assay will receive the same clinical interpretation as those in the pivotal trial.

Coordinated Submission and Labeling Alignment

One of the most critical steps in co-development is ensuring synchronized submission of the drug and diagnostic. The therapeutic product label must reference the companion diagnostic, and the diagnostic IFU (Instructions for Use) must include the specific drug indication.

FDA and EMA both require tight integration of regulatory documentation, including:

• Shared clinical trial data (Module 5)
• Analytical validation reports
• Risk management and post-approval surveillance plans

Explore detailed submission checklist templates at PharmaSOP.in.

Commercialization and Post-Market Surveillance

Once approved, both drug and CDx must maintain post-market performance. This includes:

• Ongoing QC testing of the assay
• Real-world effectiveness monitoring
• Adverse event reporting for both drug and diagnostic
• Label updates based on emerging data

In the EU, CDx manufacturers must report performance issues to both the notified body and competent authority under IVDR Article 82.

Challenges in Co-Development

Despite its advantages, co-development presents challenges:

• Misalignment of development timelines between drug and diagnostic
• Cross-border regulatory complexity (FDA vs EMA)
• Sample scarcity for rare biomarkers
• IP and commercial agreement disputes

Early planning and risk-based prioritization are essential to mitigate these issues.

Conclusion

The co-development of drugs and companion diagnostics is central to advancing personalized medicine. Sponsors must foster early collaboration between clinical, regulatory, and diagnostic teams, align trial designs, and synchronize regulatory submissions. A proactive co-development strategy not only streamlines approval timelines but also maximizes therapeutic impact for biomarker-defined patient populations.