Sergio Vázquez,1 Joaquín Casal,2 Francisco Javier Afonso Afonso,3 José Luis Fírvida,4 Lucía Santomé,5 Francisco Barón,6 Martín Lázaro,7 Carolina Pena,7 Margarita Amenedo,8 Ihab Abdulkader,9 Carmen González-Arenas,10 Laura Fachal,11 Ana Vega11 On behalf of the Galician Lung Cancer Group (GGCP)1Medical Oncology Department, Lucus Augusti University Hospital, Lugo, 2Medical Oncology Department, University Hospital Complex of Vigo, Pontevedra, 3Medical Oncology Department, University Hospital Complex of Ferrol, Ferrol, 4Medical Oncology Department, University Hospital Complex of Ourense, Ourense, 5Medical Oncology Department Povisa Hospital, Vigo, 6Medical Oncology Department, University Hospital Complex of Santiago de Compostela, Santiago de Compostela, 7Medical Oncology Department, Hospital Complex of Pontevedra, Pontevedra, 8Medical Oncology Department, Oncology Center of Galicia, A Coruña, 9Anatomical Pathology Department, University Hospital Complex of Santiago de Compostela, Santiago de Compostela, 10AstraZeneca, Madrid, 11Galician Public Foundation of Genomic Medicine-SERGAS, Santiago de Compostela Clinic Hospital, Santiago de Compostela, Spain Purpose: This study aimed to assess the incidence of mutations in the epidermal growth factor receptor (EGFR) gene in non-small-cell lung cancer (NSCLC) patients in the Galician region of Spain and the clinical management and outcome of patients carrying EGFR mutations. Patients and methods: All newly diagnosed advanced or metastatic NSCLC patients were screened for EGFR mutations in matched tumor samples (tissue or cytology specimens) and serum samples. Results: Of 198 patients screened for EGFR mutations in tumor samples, 184 had evaluable data and, of these, 25 (13.6%) had EGFR mutations (84% sensitizing mutations). EGFR mutation was found in serum in 14 (8.1%) patients (of 174 evaluable). Compared to matched tumor tissue, serum EGFR mutation testing specificity and sensitivity were 99% and 52%, respectively. All but two patients received gefitinib. Median progression-free survival and overall survival were 10 (95% confidence interval: 4.8–15.3) months and 17.8 (95% confidence interval: 13.9–21.6) months, respectively, in patients carrying sensitizing mutations. Conclusion: The incidence of EGFR mutations in Galicia is consistent with previous data in Spain. Our results also support the feasibility of EGFR testing to guide treatment decision making using tumor tissue or cytology samples, or serum samples if tumor specimens are unavailable. These findings also confirm that first-line gefitinib is an active treatment option in Caucasians with EGFR mutation-positive NSCLC. Keywords: epidermal growth factor receptor, EGFR tyrosine inhibitors, TKIs, EGFR gene mutation, EGFR mutation testing, non-small-cell lung cancer