Osimertinib mesylate is a kinase inhibitor that targets the epidermal growth factor receptor (EGFR). It binds irreversibly to specific mutant forms of EGFR, including T790M, L858R, and exon 19 deletions, at significantly lower concentrations than it does to the wild-type receptor. This selective targeting is crucial for its efficacy. Two pharmacologically active metabolites, AZ7550 and AZ5104, also contribute to its inhibitory profile.

Osimertinib is indicated for the treatment of patients with metastatic EGFR T790M mutation-positive non-small cell lung cancer (NSCLC) who have progressed on or after EGFR tyrosine kinase inhibitor therapy. It is also used as adjuvant therapy after tumor resection in patients with EGFR exon 19 deletions or exon 21 (L858R) substitution mutations. Unlike other TKIs, osimertinib is active against cancer cells with the T790M resistance mutation. It is administered as a once-daily oral tablet and has shown efficacy in preclinical models, including those with brain metastases. Osimertinib represents a significant advancement in the targeted treatment of EGFR-mutated lung cancer.