• Taro Koba, Takashi Kijima, Takayuki Takimoto, Haruhiko Hirata, Yujiro Naito, Masanari Hamaguchi, Tomoyuki Otsuka, Muneyoshi Kuroyama, Izumi Nagatomo, Yoshito Takeda, Hiroshi Kida, and Atsushi Kumanogoh.
• aDepartment of Respiratory Medicine, Allergy and Rheumatic Diseases, Osaka University Graduate School of Medicine bDepartment of Immunopathology, Immunology Frontier Research Center, Osaka University, Japan.
• Medicine (Baltimore). 2017 Feb 1; 96 (6): e6087.

RationaleMost of nonsmall cell lung cancer (NSCLC) patients harboring epidermal growth factor receptor (EGFR) activating mutations eventually acquire resistance to the first EGFR-tyrosine kinase inhibitors (TKIs) therapy after varying periods of treatment. Of note, approximately one-third of those patients develop brain metastases, which deteriorate their quality of life and survival. The effect of systemic chemotherapy on brain metastases after acquisition of EGFR-TKI resistance is limited, and thus far, whole-brain radiation therapy, which may cause the harmful effect on neurocognitive functions, has been the only established therapeutic option for especially symptomatic brain metastases. Osimertinib is a third-generation oral, potent, and irreversible EGFR-TKI. It can bind to EGFRs with high affinity even when the EGFR T790M mutation exists in addition to the sensitizing mutations. Its clinical efficacy for NSCLC patients harboring the T790M mutation has already been shown; however, the evidence of osimertinib on brain metastases has not been documented well, especially in terms of the appropriate timing for treatment and its response evaluation.Patient Concerns, Diagnoses, And InterventionsWe experienced 2 NSCLC patients with the EGFR T790M mutation; a 67-year-old woman with symptomatic multiple brain metastases administered osimertinib as seventh-line chemotherapy, and a 76-year old man with an asymptomatic single brain metastasis administered osimertinib as fifth-line chemotherapy.OutcomesThese patients showed great response to osimertinib within 2 weeks without radiation therapy.LessonsThese are the first reports to reveal the rapid response of the brain metastases to osimertinib within 2 weeks. These cases suggest the possibility that preemptive administration of osimertinib may help patients to postpone or avoid radiation exposures. In addition, rapid reassessment of the effect of osimertinib on brain metastases could prevent patients from being too late to receive essential radiotherapy.

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