Companion Diagnostics and Complementary Diagnostics in Clinical Practice: Better Medicine or Competitive Disadvantage?

We are pleased to present the second installment in our recurring column, Pharma Insights. This month we take a look at an interesting twist in how the use of complementary and companion diagnostics is playing out in real-world clinical practice. In a health care system that increasingly seeks to more precisely target therapeutic approaches to diseases, diagnostic testing is the key to unlocking greater value in pharmacotherapy. Two classes of diagnostic tests—companion and complementary diagnostics—have emerged to address this need.

Companion diagnostic tests are central to personalizing drug treatment and increasingly have become the focus of new drug development in cases when it is possible to identify the actual target of drug action. Companion diagnostics provide information that is essential for the safe and effective use of a corresponding therapeutic product; therefore, the test is required by the drug’s “Indications for Use.” 

The complementary diagnostic concept is much newer. In mid-2015, the Food and Drug Administration (FDA) preliminarily defined this classification as a test that identifies a subset of patients that respond particularly well to a drug or that provides information that aids in risk/benefit assessments of treatment but is not a prerequisite for receiving the drug. Accordingly, the test is not required by the drug’s “Indications for Use,” but it may be mentioned elsewhere in the drug’s labeling. 


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Adoption of these tests into routine clinical practice has not been as straightforward as you might think. A well-known example is clopidogrel (Plavix; Bristol-Myers Squibb), a commonly used antiplatelet agent. The product’s label suggests that testing for a specific genetic factor (CYP2C19) can be used as an “aid” in determining therapeutic strategy. It turns out that patients with this specific genetic factor do not see the same benefits of therapy as those without it, namely, reduced risk of heart attacks and strokes. Although this has become a black box warning included in the label, testing is not specifically required in the “Indications for Use.”

Manufacturers of competitor products whose effects are not influenced by the presence of the genetic factor have seized upon this as a basis for marketing their differentiation from clopidogrel. Although fairly straightforward clinically, the situation becomes more complex because clopidogrel is now generically available and, thus, much less costly than its branded competitors. As such, many providers and plans haven’t pushed to more aggressively identify those likely non-responders to clopidogrel.

The oncology market has an exploding number of treatments with genetic markers, and, increasingly, companion and complementary diagnostics are driving or guiding therapeutic decision-making. We are now beginning to see competitive products with similar indications that have variances in the types of diagnostic criteria applied, and we are seeing distinct promotional strategies evolving around those criteria as well.

It is too early to reach sweeping conclusions on the value of these variances in diagnostic application; for example, whether companion diagnostics are the keys to better medicine or commercial burdens, or whether complementary diagnostics are meaningful only for academic clinicians isolated from routine clinical practice. Clinicians are still determining the real-world value of the information these tests provide and how best to use them in the context of patient needs and practice pressures. Payers don’t yet know if they can rely on these tests to sufficiently drive coverage and medical policy decision-making. We will continue exploring the application of these tests to therapeutic selection in a future installment of Pharma Insights