Osimertinib is a member of the class of aminopyrimidines that is 4-(1-methylindol-3-yl)pyrimidin-2-amine in which one of the amino hydrogens is replaced by a 2-methoxy-4-[2-(dimethylamino)ethyl](methyl)amino-5-acrylamidophenyl group. Used (as the mesylate salt) for treatment of EGFR T790M mutation positive non-small cell lung cancer. It has a role as an antineoplastic agent and an epidermal growth factor receptor antagonist. It is a secondary carboxamide, a member of acrylamides, a member of indoles, a monomethoxybenzene, an aminopyrimidine, a substituted aniline, a secondary amino compound, a tertiary amino compound and a biaryl. It is a conjugate base of an osimertinib(1+).