A lead-in phase of 6 patients will be initiated prior to the formal phase II study. The planned sample size is 27 patients (lead-in and phase II).~The primary objective of the study is to demonstrate that S-1 fixed dose 40 mg BD is safe and effective in EGFR metastatic lung cancer resistant to Osimertinib in terms of best overall response (BOR) The secondary objective of this study will be to further analyse the Disease Control Rate at stipulated timepoints (6,12 and 24 months), Progression-free survival and also the Toxicity by CTCAE 5.0.
The objective of this study is to determine overall response rate to combination of S-1 and Osimertinib in treatment-resistant EGFR mutant lung cancer.