In case of isolated CNS progression which may or may not be accompanied by asymptomatic systemic progression, AZD9291 dose will be escalated to 160 mg once daily. For patients whose intracranial disease will progress further, brain radiotherapy (in the form of SRS or WBRT) will be administered; treatment with AZD9291 will be interrupted and re-initiated at a standard dose after the end of radiotherapy course in the absence of symptomatic systemic progression. The treatment will be continued until symptomatic systemic progression, unacceptable toxicity or further intracranial progression following brain radiotherapy administration (whichever occurs first). All patients will be followed until death or 5 years.