In Part A, each patient will receive a single oral dose of osimertinib 80 mg (given as a tablet). Where possible, patients will check into the clinic on Day -1, the evening prior to dosing (Day 1), and remain resident until 24 hours after the dose of osimertinib (Day 2) for collection of blood samples and 24-hour pooled urine for PK analysis during this time. Samples will be analysed to determine the concentrations of osimertinib and metabolites (AZ5104 and AZ7550) in plasma, urine, and plasma ultrafiltrate (PUF). Patients will then return to the clinic as outpatients for assessments on Day 3 (48 hours), Day 4 (72 hours), Day 6 (120 hours), Day 8 (168 hours) and Day 10 (216 hours).