Three laboratories will participate in the study. Each laboratory will analyze the same samples by different methodologies according to the flow indicated in figure 1. This design will allow comparing the agreement performance of different methods available for T790M identification in circulating-free DNA isolated from peripheral blood.

Three blood samples per patient will be collected once at the time of progression, assessed by CT Scans according to RECIST criteria v.1.1 and before the patients start a new treatment The blood samples (5-10 mL each) will be collected in one Cell-Free DNA BCT Streck® and 2 PTT EDTA K2 (BECTON DICKINSON) collection tubes.

All samples will be labeled properly with the patient identification number and date of extraction. These samples will be stored and distributed through the 3 participating laboratories until completion of all the analyses, according to the flowchart in Figure 1. These samples will be registered in the samples collection of the Institute of Health Carlos III Registry. These samples will be kept in each participant laboratory after the completion of the RING study and the patient will be informed of that in the patient information sheet and informed consent.

cfDNA will be extracted using as starting volume 1 ml of plasma with a Maxwell® RSC instrument (Promega), using the Maxwell® RSC cfDNA Plasma Kit (MR), as specified by the manufacturer or with a Qiasymphony instrument (Qiagen company). Additionally, for BEAMing analysis, 3 ml of plasma will be used for cfDNA isolation using the the QIAamp® Circulating Nucleic Acid Kit (Qiagen company), following the manufacturer instructions.

Circulating free DNA from peripheral blood sample is an adequate source for T790M resistance mutation testing. However, comparison across different platforms has been scarcely reported. Discordant results for EGFR biomarker testing could impact patient management.

Inclusion Criteria:

• Patients diagnosed with EGFR mutant, stage IIIB and IV non small cell lung cancer and who have progressed assessed by CT Scans according to RECIST criteria v.1.1 to first or second generation EGFR tyrosine kinase inhibitors (TKIs) (e.g. gefitinib, erlotinib, afatinib) including patients who received a chemotherapy line before TKI treatment. Samples have to be drawn before the patient starts a new treatment,
• Patients have to sign the informed consent of the study
• Patients aged ≥ 18 years.

Exclusion Criteria:

• Patients progressing to third generation EGFR TKIs (e.g. Osimertinib (TKI))
• No possibility of venipuncture.

EGFR mutant non small cell lung cancer patients.