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Companion diagnostic tests: One step closer to precision medicine

A companion diagnostic test accompanies a targeted therapy to fight a given disease. It is used primarily in oncology, but it could also be applied to neurological diseases. The purpose of these tests is to define the subpopulations of patients likely to respond favorably to the treatment in question, by identifying markers in patients to predict treatment response. It not only improves the effectiveness, but also the safety, of the treatment for the patient.

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The FDA (US Food and Drug Administration) defines a companion diagnostic test as “a medical device, often an in vitro diagnostic (IVD), which provides information that is essential for the safe and effective use of a corresponding drug or biological product.”1

At Servier, our ambition is to become a key player in precision medicine. We are convinced that a personalized approach to medicine significantly improves therapeutic management and patient quality of life throughout the treatment journey.

Companion diagnostic tests are in line with this vocation. With a diagnostic test adapted to the treatment, we will be able to identify the patients who will respond positively sooner, and thus provide them with the most suitable treatment more quickly.

For more information, read our insight: Understanding companion diagnostic tests

First of all, you need to understand that the treatments we develop are targeted therapies, i.e., they are intended for very specific pathologies associated with molecular anomalies, such as genetic mutations, or the overexpression of a protein in a tumor, etc. The modifications identified are then used as biomarkers.
When a group of patients presents an identified or characterized anomaly, we need to develop what we call a suitable “drug/test” pair to be able to propose the most favorable treatment to these patients.

Good to know

A companion diagnostic test is performed on a sample taken from the patient, often a tumor tissue biopsy or a blood/plasma sample. The choice of technology and the test methodology depends on many factors and may be a genomic test (PCR, NGS) or a protein test (ICH).

As part of the development of targeted therapies in oncology, in Europe, the United States, Japan and China it is mandatory that a companion diagnostic test be developed at the same time. This process is governed by a regulatory framework that ensures the benefit provided to patients. Companion diagnostic test efficacy depends on reliability, the safety it guarantees for the patient, and finally the speed with which results are obtained. The process is therefore just as strict as development of the associated therapeutic treatment that takes place simultaneously. The goal of a synchronized approach is to prove compatibility between the targeted therapy and the associated companion diagnostic test, and their market introduction all at once.


Today, more than 170 companion diagnostic tests have been approved by the FDA, primarily in oncology2.

The objective of the preclinical and clinical development phases is to demonstrate the ability of the identified biomarker to predict the improved efficacy of the associated (targeted) treatment in a defined pathology. Companion diagnostic test development will follow very strict and regulatory validation steps (under design control), particularly in scientific, analytical and clinical terms.

At the end of clinical development and the pivotal trial assessing the efficacy of the “drug/test” pair, the test will be submitted to the relevant health or medicine regulatory authorities at the same time as the associated targeted therapy.

Finally, the choice of partner for companion diagnostic test development and marketing is yet another challenge. As a pharmaceutical group, our goal is to provide patients with treatments, no matter where they live. This is why we work with experienced partners that have a global footprint and thorough knowledge of local regulatory constraints.

Companion diagnostic tests are a promising application of more targeted, personalized medicine. They allow us to provide the right drug to the patient, right from the start.

There are many benefits for patients. The test allows the most suitable treatment to be administered more quickly, which in short, significantly improves patient quality of life.

[1]  US Food and Drug Administration – Medical devices – June 2023 (

[2] FDA –