Guidelines for the treatment of non-small cell lung cancer adenocarcinoma positive in epidermal growth factor mutations indicate tyrosine kinase inhibitors. There are currently three tyrosine kinase inhibitors that can be used as first line treatment: gefitinib, erlotinib and afatinib. Regarding erlotinib and afatinib dosage can be modified in the case of severe adverse effects. In the case of disease relapse investigation for T790M mutation has to be made either with re-biopsy or liquid biopsy and osimertinib has to be administered when T790M is diagnosed. Based on a case series we indicate which is the best approach for T790M mutation.