Osimertinib dimesylate (Mereletinib dimesylate, AZD-9291 dimesylate) is a potent, mutant-selective, irreversible inhibitor of EGFR kinase activity with an IC50s of 12 and 1 nM against EGFRL858R and EGFRL858R/T790M, respectively. It demonstrates anti-tumor activity in xenograft and transgenic T790M EGFR mutant models, supporting its use in non-small cell lung cancer (NSCLC) research.