e23035Background: NSCLC patients harboring EGFR mutations are able to receive approved tyrosine kinase inhibitors (TKIs) but to better assess the treatment responses new tools are needed. Liquid biopsy is a promising one. Exosomes are the latest discovered component, containing reliable tumor informations. We performed a follow-up analysis of selected micro-RNAs (miRNAs), EGFR mutation related , in exosomes isolated from plasma of metastatic NSCLC EGFR mutated pts receiving osimertinib, in order to evaluate their potential prognostic biomarker features Methods: After ethical committee approval, for institutional study, 1 ml plasma sample of 2 EGFR positive NSCLC pts were used as exosome source for each follow-up time point during osimertinib treatment within a PK study (NCT02157883). Exosome were isolated through commercial-kit or sucrose density-gradient ultracentrifugation. After exosome characterization by Western-Blot, Transmission and Scanning Electron Microscopy, a panel of selected miRNAs (has-miR-...