The role of companion diagnostics (CDx) in targeted therapies
The role of companion diagnostics (CDx) in targeted therapies
Targeted therapies have transformed modern medicine by aligning treatment with the biological characteristics of a patient’s disease. At the center of this approach are companion diagnostics (CDx)—tests that identify biomarkers to guide treatment decisions. Together, targeted therapies and CDx support more precise, data driven care, particularly in oncology and other biomarker led indications.
What are companion diagnostics (CDx)?
CDx are in vitro diagnostic tests that provide information required for the safe and effective use of a specific therapeutic product. Regulatory agencies such as the FDA and EMA recognize CDx as critical tools for identifying patients who are more likely to benefit from a targeted therapy, those who may be at higher risk of adverse reactions, or those whose response to treatment should be monitored.
Most CDx are developed alongside targeted medicines, reflecting the growing recognition that many diseases—especially cancers—are biologically diverse rather than uniform. This shift has accelerated the move away from broad treatment approaches toward biomarker guided strategies.
Why companion diagnostics matter?
Traditional treatment models often rely on population level averages, which can result in variable outcomes across patients. CDx help address this challenge by enabling patient stratification based on molecular or genetic markers. This approach supports more informed treatment selection and helps reduce exposure to therapies unlikely to provide benefit.
- Precision medicine enabler: Transforms treatment from a "one-size-fits-all" approach to a personalized model, improving success rates for drugs that might otherwise fail in an unselected patient population.
- Diverse methodologies: While molecular diagnostics (genetic information) are common, CDx can also be protein-based (immunohistochemistry), metabolite-based, or leverage imaging tools.
- Commercial & economic driver: Enables smaller, faster, and less expensive clinical trials by targeting specific populations; however, it may require complex reimbursement strategies to demonstrate value to payers.
From a development perspective, the use of CDx allows clinical trials to focus on more defined patient populations. This can improve the clarity of trial outcomes and support more efficient development pathways. As a result, CDx have become a foundational element of precision medicine programs.
Coordinated development of drugs and diagnostics
CDx typically follow a coordinated development pathway with their associated therapies. Early in development, exploratory assays may be used to investigate potential biomarkers. As programs advance and biomarker data begins to influence trial design or patient selection, these assays transition into regulated diagnostic devices.
Regulatory guidance encourages alignment between drug and diagnostic timelines, particularly when diagnostic results influence trial enrollment or primary endpoints. This coordinated approach supports smoother regulatory review and helps align evidence generation for both products.
Regulatory and clinical considerations for companion diagnostics
CDx are subject to rigorous analytical and clinical validation requirements. In Europe, this includes compliance with the In Vitro Diagnostic Regulation (IVDR), while in the United States, CDx undergo FDA premarket review. These frameworks focus on demonstrating that the diagnostic reliably identifies the intended biomarker and supports appropriate clinical decision making.
Clinically, the use of validated diagnostics in pivotal trials strengthens the link between biomarker status and treatment outcomes—an essential factor for regulatory submissions and post approval use.
Future of companion diagnostics
Advances in technologies such as next generation sequencing are expanding the scope of CDx enabling the assessment of multiple biomarkers from a single sample. This evolution supports more comprehensive molecular profiling and aligns with the increasing complexity of targeted therapy pipelines.
As targeted therapies continue to expand beyond oncology into areas such as immunology and rare diseases, CDx will remain central to precision based development and patient care strategies.
What places Fortrea as a unique service provider?
Fortrea’s position as a specialized MedTech CRO with deep diagnostic experience, independent of any specific drug-producing company, offers unique advantages:
- End-to-end diagnostic journey: Fortrea covers the full spectrum from analytical validation to clinical evidence generation, supporting regulatory submissions (FDA/EMA/IVDR) and post-market surveillance.
- Independent, customer-centric model: As a CRO, Fortrea operates as an extension of the customer’s team, providing unbiased support to both pharma and diagnostic developers without conflicts of interest from in-house development.
- Global reach with local insight: Provides niche-level support for diagnostic trials across global regions (US, EU, APAC), with expertise in navigating regional regulatory requirements such as EU IVDR.
- Specialized in advanced therapies: Leverages data from its proprietary cell therapy site intelligence platform and has experience handling high-potency, complex diagnostic technologies.
- Minimized rework and accelerated timelines: Dedicated specialists focus on safeguarding sample integrity and optimizing study protocols to prevent costly retesting and accelerate regulatory approval timelines.
- Comprehensive regulatory knowledge: Offers expertise in managing the transition from laboratory-developed tests (LDTs) to approved in vitro diagnostics (IVDs).
Learn how Fortrea supports biomarker-driven development across the clinical lifecycle—helping sponsors align diagnostics and targeted therapies from early strategy through late-phase execution. Explore more .