Objective: The primary objective of this study is to evaluate the disease control rate (DCR; confirmed complete response (CR) or partial response (PR), or stable disease (SD)) of gefitinib using Response Evaluation Criteria in Solid Tumours (RECIST) version 1.1 in patients with activating sensitising Epidermal Growth Factor mutation positive (EGFR M+) NSCLC. The secondary objectives of the study are: objective response rate (ORR) according to RECIST, progression free survival (PFS) according to RECIST, overall Survival (OS), EGFR Mutational status of tumour tissue both activating and resistance EGFR mutations analysis and the association between the Veristrat assay (Biodesix) and both PFS and OS will be assessed.