Lyudmila Bazhenova, MD of the University of California, San Diego discusses T790M mutation and the role of osimertinib in the first line treatment of NSCLC. T790M mutation testing happens automatically when EGFR mutation testing is done. In EGFR mutation testing, the whole EGFR gene in exon 18, 20, 21 is usually get in sequence. So, if the patient has T790M found at the time of diagnosis and not as a resistance mechanism, this can be found with the typical EGFR sequencing.
It is important to remember that, osimertinib is not just a T790M drug, but it has significant activity against sensitizing EGFR mutations. So, the FDA approval for the T790M testing helps in choosing the second line therapy, if the first-line is EGFR TKI like erlotinib or gefitinib. However, for the decision whether or not to use osimertinib first-line, the T790M testing doesnt really matter because osimertinib works even without the T790M mutation.