However, the distinction between how the two different types of diagnostic tests are intended to be used still confuses many physicians and healthcare professionals
Companion diagnostics are well-known to medical laboratorians. However, the new-breed of complementary diagnostics might not be as familiar. As the pharmaceutical pipeline increasingly becomes filled with test-dependent new drug therapies, medical laboratories and anatomic pathology groups may need to sharpen their understanding of companion and complementary diagnostics to broaden their laboratory test portfolios and keep pace with the growing demand for these new diagnostics.
Currently in the US, 30 companion diagnostic assays have been approved governing the use of 19 therapeutic drugs, according to a recent NCBI table published in Clinical and Translational Science.
The FDA defines a companion diagnostic as a “medical device, often an in vitro device, which provides information that is essential for the safe and effective use of a corresponding drug or biological product. The test helps a healthcare professional determine whether a particular therapeutic product’s benefits to patients will outweigh any potential serious side effects or risks.”
Because a companion diagnostic device is “essential for the safe and effective use” of the drug to which it has been assigned, it is identified on the drug’s product label.
The anti-HER2 drug Herceptin, for example, is a commonly prescribed breast-cancer therapy drug that in its various forms comes with one of 11 companion diagnostic devices. As a requirement of Herceptin’s Food and Drug Administration (FDA) approval, the agency requires pathologists to use a companion diagnostic test to confirm a patient’s over expression of HER2 (human epidermal growth factor receptor2) protein before prescribing Herceptin. The other HER2-directed therapies have their own assigned companion diagnostic.
Complementary Diagnostics Is a Growing Opportunity for Clinical Labs
Now, nearly two decades after companion diagnostics first made headlines, pathologists are encountering a new concept—complementary diagnostics. Unlike companion diagnostics, complementary diagnostics aid the therapeutic decision process, but are not required when prescribing the corresponding drug.
In an interview with Dark Daily, Debra Harrsch, President and Chief Executive Officer of Philadelphia-based Brandwidth Solutions, noted that the addition of complementary diagnostics adds a layer of complexity to the diagnostics landscape for pathologists and other healthcare professionals.
“The diagnostics landscape is not only expanding in size and scope, it is also becoming increasingly complex as growth in biomarker– and genomic-based test strategies fuels progress in personalized medicine,” she stated.
Peggy Robinson, US Vice President of ANGLE plc, a global liquid biopsy diagnostic company, explained that the lack of a regulatory link to a specific testing technology is the critical distinction between a complementary and a companion diagnostic.
“A companion diagnostic is one of the gateways for you to receive a drug,” Robinson stated in the Dark Daily interview. “A complementary diagnostic can aid your physician in helping to determine what level of therapy would be appropriate for you, but it is not required.”
Pairing Clinical Laboratory Tests with Complementary Diagnostics
In 2015, Dako’s PD-L1 IHC 28-8 pharmDX immunohistochemistry test, which determines PD-L1 protein in non-squamous non-small cell lung cancer, became the first FDA-approved complementary diagnostic, when it was paired with the drug Opdivo (Nivolumab).
At that time, Christopher Fikry, MD, then Vice President, Oncology, of Quest Diagnostics (NYSE:DGX), praised the FDA’s introduction of the first complementary diagnostic. He noted in a statement that it would “give physicians greater understanding of treatment expectations with Opdivo and helpful information to communicate to patients.”
Clinical Laboratories Can Add Value to Their Patients’ Healthcare
The challenge for clinical laboratories and pathology groups will be keeping pace with a rapidly expanding catalog of available diagnostic tests. While the number of drugs (two) with FDA-approved complementary diagnostic tests remains small, Peter Keeling, CEO of Diaceutics, a global advisory group for the laboratory, diagnostic, and pharmaceutical industries, predicts that number will be rising.
In a 2016 webinar on companion versus complementary diagnostics, Keeling pointed out that 50% to 90% of products in development through 2020 at the top 10 pharmaceutical companies are test dependent. This highlights the importance of targeted therapies designed to advance the goals of personalized medicine.
Clinical Labs Can Build Out Test Menus with Complementary Diagnostics
“Laboratorians need to understand what type of technologies they are using to employ these diagnostics,” Robinson told Dark Daily. “As laboratory managers build out their test portfolios, they should be looking at the technology and asking, ‘Can I integrate that into my laboratory?’ so that when a new test comes out, they can offer it.”
Meanwhile, healthcare professionals have more work to do to understand the differences between companion versus complementary test labeling. In his webinar, Kelly noted that in a poll of 30 Opdivo/Keytruda prescribers, Diaceutics found:
- 40% of prescribers surveyed did not understand the differences between the PD-L1 test labels for Keytruda (Pembrolizumab), which requires a companion diagnostic, and Opdivo, which has an associated complementary diagnostic;
- 60% were unclear about the role of complementary testing; and
- 50% said their therapy decisions would be impacted if a laboratory used for PD-L1 testing offered only one test.
Harrsch told Dark Daily that “time will tell” whether complementary diagnostics can match the impact of companion diagnostics in improving healthcare outcomes.
Future of Complementary Diagnostics Still Uncertain
“The role companion diagnostics can have in driving personalized medicine is already leaving its mark with drugs such as Herceptin,” she said. “The impact of complementary diagnostics, and how the two types of tests come to share the stage, awaits to be seen.”
As the market for companion and complementary diagnostics expands beyond targeted therapies for oncology, clinical laboratories and pathology groups can position themselves to “add value” to their patients’ journey through the entire healthcare continuum. Robinson believes one key for pathologists going forward will be maintaining a “close working relationship” with client physicians in order to plan for future test offerings.
—Andrea Downing Peck