Osimertinib: A third-generation tyrosine kinase inhibitor for treatment of epidermal growth factor receptor-mutated non-small cell lung cancer with the acquired Thr790Met mutation

Osimertinib is a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) approved for the treatment of metastatic EGFR T790M mutation-positive non-small cell lung cancer (NSCLC) in patients failing previous TKI therapy. The T790M mutation is an acquired resistance mechanism found in over half of patients with NSCLC progressing on first-generation TKIs. First- and second-generation TKIs do not inhibit the T790M mutation at clinically relevant concentrations. Osimertinib is selective for mutated forms of EGFR, including the TKI-sensitizing mutations L858R and exon 19 deletions, as well as the acquired T790M resistance mutation. In a trial comparing osimertinib to platinum doublet therapy among patients with the T790M mutation progressing on first-line TKI therapy, median progression-free survival was significantly longer in patients receiving osimertinib. Osimertinib has a favorable safety profile compared to platinum-doublet chemotherapy. Common adverse events include diarrhea, skin rash, dry skin, and paronychia; however, because it spares wild-type EGFR, these toxicities appear to occur with less frequency and severity compared to other TKIs. Serious, but rare, adverse events include pneumonitis, interstitial lung disease-like events, QT interval prolongation, and reduced ejection fraction. Osimertinib has the unique ability to distribute readily into brain tissue compared with other TKIs, giving it a potential role in the treatment and/or prevention of CNS metastases; future studies are warranted in this area. An ongoing study evaluating osimertinib versus first-generation TKIs as first-line treatment for patients with EGFR mutation-positive NSCLC may help to define the role of osimertinib as front-line therapy.