[Osimertinib for an Elderly Patient with Adenocarcinoma of the Lung Harboring EGFR T790M Mutation Diagnosed Using a Pleural Fluid Cell Block].

A 90-year-old woman was referred to our hospital because of dyspnea with pleural effusion that was detected using a chest X-ray. Pleural fluid cell block specimens from the left pleural effusion were shown to be an adenocarcinoma harboring an epidermal growth factor receptor(EGFR)gene mutation(L858R). Erlotinib was administered and the patient responded to treatment for 15 months. Subsequent re-accumulation of the left pleural effusion was detected, and re-evaluation using cell block specimens revealed EGFR T790M mutation positivity. Osimertinib was initiated and the patient responded to treatment for 11 months. Re-evaluation of the left pleural effusion upon failure of osimertinib treatment revealed EGFR T790M mutation negativity. Hence this report summarizes the case of osimertinib therapy being administered to a 90-year-old patient who had EGFR T790M mutation positivity based on a pleural fluid cell block.