At the end of Part B, those patients with severe renal impairment who are deemed to be gaining clinical benefit from osimertinib will enter the continued access phase. Patients with normal renal function can enter the continued access phase immediately after completing Part A (ie, collection of the last PK sample scheduled on Day 10 of Part A). During the continued access phase, patients may continue to take osimertinib 80 mg once daily, if patients and the Investigator deem it appropriate, or until such time as their disease progresses, the Investigator believes the patients are no longer deriving clinical benefit, or patients stop taking osimertinib for any other reason. No clinical data, other than serious adverse events (SAEs) that may be related to the investigational product (IP), will be collected during this phase.