In a phase 2 study involving radiotherapy-naive adult patients diagnosed with T790M EGFR mutation-positive NSCLC and CNS metastasis, who had been previously treated with EGFR tyrosine kinase inhibitors, the plasma and CSF concentrations of osimertinib and its pharmacologically active metabolite were assessed in seven participants on day twenty-two of osimertinib therapy. This evidence concerns the gene EGFR and non-small cell lung carcinoma.