Background: Progression-free survival (PFS) and response to EGFR tyrosine kinase inhibitors (TKIs) vary in p with NSCLC driven by EGFR mutations. In our experience, high BRCA1 mRNA expression was associated with shorter PFS in EGFR-mutant p treated with erlotinib. We hypothesized that since olaparib downregulates BRCA1 expression, the addition of olaparib to gefitinib could improve PFS in these p. Methods: This is a Phase IB dose escalation study to identify the maximum tolerated dose (MTD), dose limiting toxicity (DLT), pharmacokinetics, and clinical activity of orally administered olaparib in combination with gefitinib in EGFR-mutant advanced NSCLC p. In a standard 3+3 design, p were treated with gefitinib 250mg once daily plus olaparib tablets at escalating doses ranging from 100mg BID to 250mg TDS during a 28-day cycle. Results: 18 p have been included across four dose levels of olaparib: 100mg BID (3), 200mg BID (6), 200mg TDS (3) and 250mg TDS (6). Median age, 69; male, 4; PS 0, 17; EGFR TKI treatment-naïve, 10. Toxicities: anemia (66.6%), leucopenia (33.3%), nausea (33.3%), diarrhea (33.3%), asthenia (27.7%), rash (22.2%) vomiting (11%), decreased appetite (16%), and hyperlipasemia (5.5%). Most toxicities were G1-2; G3 drug-related events included leucopenia (1) and anemia (3). No DLT at dose levels 1, 2, and 3; 1 DLT at dose level 4 (G3 anemia and repeated blood transfusion within 4-6 weeks). Few dose reductions or interruptions were needed. 1 p died due to pulmonary embolism unrelated to treatment. Partial responses (PR) were observed in 7 p (41.1%), all EGFR TKI-naïve; stable disease (SD) in 7 (41.1%), most previously treated; progressive disease (PD) in 3 (17.6%), all previously treated. Durable PR and SD were observed in EGFR TKI-naïve and previously treated p. 8 patients are still on treatment. Enrollment to dose level 4 will be completed in February 2013. Conclusions: This phase IB trial of gefitinib plus olaparib, has confirmed the activity and tolerability of the combination. The final recommended dose of olaparib is expected to be between 200 and 250 mg TDS. A phase II randomized trial in treatment-naïve EGFR-mutant advanced NSCLC will be opened in 2013. Clinical trial information: NCT0151317.