A drug used to treat non-small cell lung cancer that has spread to other parts of the body and has certain mutations (changes) in a gene called epidermal growth factor receptor (EGFR). It is used in patients whose cancer has not been treated or has gotten worse during or after treatment with another anticancer drug that blocks EGFR. It is also being studied in the treatment of other types of cancer. Osimertinib mesylate blocks certain proteins made by the mutated EGFR gene, which may keep cancer cells from growing and may kill them. It is a type of kinase inhibitor. Also called Tagrisso.