Companion Diagnostics

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The page below is a sample from the LabCE course Precision Medicine-Molecular Mechanisms of Cancer Development and Actionable Genes. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Companion Diagnostics

Targeted therapy is a great option for a patient if they have the corresponding biomarker. However, if the patient does not have the biomarker that is targeted by the drug, they are less likely to respond to that type of treatment. This is where the laboratory plays a crucial role in oncology treatment. There are tests called companion diagnostics that are linked to the FDA-approval for certain targeted therapies. In these cases a specific laboratory test must be used to determine the presence or absence of the biomarker for the safe and effective use of that drug.
A great example of this is with epidermal growth factor receptor (EGFR) and tyrosine kinase inhibitors (TKI). PCR or NGS is used to genotype the EGFR gene in the patient's lung cancer cells. If the EGFR gene has specific mutations such as an exon 19 deletion or L858R mutation, these patients may be eligible for TKI therapy. During TKI treatment patients become resistant to treatment after approximately 12 months. PCR is performed again on a new biopsy to determine if the patient has a new resistance mutation, T790M. If the patient has this mutation they can be switched to a new TKI that acts selectively against mutated EGFR. The laboratory has a key role in assisting the provider in getting the patient on the right therapy for their lung cancer.