In contrast to chemotherapy, there are now much more targeted options for some cancers. Targeted therapy is an option if the patient has the corresponding biomarker (i.e. the proposed drug targets the specific mutation present in the patient). 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. Laboratory testing that accompanies pharmacologic treatment is referred to as "companion diagnostics". These lab tests are actually linked to, (and required) for the FDA-approval of these targeted therapies. In these cases, a specific laboratory test must be used to determine the presence or absence of the biomarker before the drug is indicated and used.
A great example of this is with epidermal growth factor receptor (EGFR) and tyrosine kinase inhibitors (TKI). PCR or NGS is first 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 are eligible for TKI therapy. During TKI treatment patients usually 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 thus has a key role in assisting the provider in getting the patient on the right therapy for their lung cancer.
