EGFR and neoplasm: The amount of ex19del, p.L858R and p.T790M EGFR mutant copies in plasma was monitored during treatment with osimertinib in 5 patients (2 with complete response to osimertinib, 2 with partial response and 1 with stable disease at first-tumor evaluation after 12 weeks) in order to gather information about the dynamics of EGFR mutational pattern as a function of therapy and time.