What is the Difference Between Companion Diagnostic and Complementary
Diagnostics?
With the accumulated understanding of disease mechanisms and molecular
diagnosis, the development of biomarkers has been accelerated. More and
more companion diagnostic and complementary diagnostics have been
approved by the U.S. Food and Drug Administration (FDA). According to
the FDA’s definition, a companion diagnostic provides
essential information for the safe and effective use of a
corresponding project, while a complementary diagnostic provides
additional information or guidance for a particular product.
Patients can obtain an assessment of the risks or benefits of drugs or
treatments from complementary diagnostics, but the recommendations
provided by complementary diagnostics are not a prerequisite for
receiving drugs or treatments.
Example of Companion Diagnostics - HER2 and EGFR
The treatment of HER2-positive breast cancer is one of the most
used companion diagnostics. About 20% of breast cancer cases in Hong
Kong are HER2-positive, and HER2-positive breast cancer
tumors grow and spread faster than other non-HER2-positive breast
cancer. Herceptin, targeted therapy for breast cancer, can only be used
effectively if the HER2 gene is found to be overexpressed. With
HER2 diagnostics, the first companion diagnostic in history, was
approved by the FDA in 1998, has brought us to the era of companion
therapy.
EGFR mutation test is another common companion diagnostic
approved by the FDA in recent years for treating patients with
EGFR mutations of non-small cell lung cancer (NSCLC).
EGFR mutations are very common among lung cancer patients in Hong
Kong. About 47% of non-small cell lung cancer patients reported an
incidence of EGFR mutation-positive2. If a patient is tested to
be EGFR mutation-positive, EGFR targeted therapies can be
used.
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