3. Previous treatment with AZD9291, or another EGFR TKI with similar profile, e.g. CO-1686 4. Major surgery within 4 weeks of inclusion 5. Radiotherapy treatment to more than 30% of the bone marrow or with a wide field of radiation within 4 weeks of inclusion 6. Subjects currently receiving (or unable to stop using) potent inhibitors or inducers of CYP3A4 7. Any unresolved toxicities from prior therapy greater than CTCAE grade 1 (with the exception of alopecia grade 2) at the time of starting study treatment.