Some time back, FDA alluded to a new category of biomarker termed “complementary diagnostic.”  This was the Agency’s first use of a categorization beyond “companion diagnostic.” Since then there have been several public announcements of new “complementary diagnostic” tests, or expanded indications for existing tests, but no definition forthcoming from FDA.

By contrast, the companion diagnostic test category has been clearly defined by FDA as an “in vitro diagnostic device or an imaging tool that provides information that is essential for the safe and effective use of a corresponding therapeutic product.”

While FDA has yet to provide a clear definition of a complementary diagnostic, the Agency appears to be happy to provide one by corporate proxy.

Last week, Roche announced the simultaneous approval of its new PD-L1 inhibitor for bladder cancer, atezolizumab (TECENTRIQ), and a new complementary diagnostic test for PD-L1 from its subsidiary Ventana.

Roche’s press release states that “PD-L1 testing is not required for the use of TECENTRIQ, but it may provide additional information for physicians and inform patient dialogue.”

Several things are interesting about this announcement:

– FDA still has yet to provide a definition of a “complementary biomarker” or “complementary diagnostic;”

– We are learning about the Agency’s perspective on this category of biomarker/test via corporate press releases;

– These press releases are exclusively about tests linked to drugs that target PD-L1;

– It is unclear whether PD-L1 expression level confers a greater or lesser chance of benefiting from PD-L1 targeted immunotherapies;


Is there any true definition of “complementary diagnostic”?  Or is it simply a way to express the industry’s (and the FDA’s) lack of understanding of the link between PD-L1 expression and immunotherapeutic benefit?

This test category clearly has a long way to go.