EGFR and non-small cell lung carcinoma: The EGFR TKI osimertinib is currently first-line therapy for patients with EGFR exon 19, exon 20 T790M, and exon 21 L858R NSCLC.12,32 Our patient's intracranial response on osimertinib suggests that her progression on mobocertinib reflects limited drug CNS penetrance as opposed to acquired resistance to therapy.