A 59-year-old smoker...diagnosed a non-small cell lung cancer (NSCLC) of adenocarcinoma subtype....Epidermal growth factor receptor (EGFR) mutations were characterized according to a sensitive method based on high-performance liquid chromatography and sequencing...The rare mutation A859T was observed. Erlotinib was introduced after a wash-out period of 4 weeks. Tolerance was excellent. Eight weeks later, CT scan demonstrated a partial response (criteria RECIST 1.1 = − 41%).