the Food and Drug Administration approved osimertinib (Tagrisso, AstraZeneca Pharmaceuticals) for adult patients with locally advanced, unresectable (stage III) non-small cell lung cancer (NSCLC) whose disease has not progressed during or following concurrent or sequential platinum-based chemoradiation therapy and whose tumors have EGFR exon 19 deletions or exon 21 L858R mutations, as detected by an FDA-approved test.

...- Patients must have adequate archival material from a previous biopsy to determine EGFR mutation status and Cripto-1 expression, or undergo a biopsy of fresh tissue of the primary cancer or a metastatic site in order to make these determinations, if archival material is...

...Documented evidence of EGFR mutation (at any time since the initial diagnosis of NSCLC) known to be sensitive to osimertinib. ...

Here, we report a case of spontaneously transformed EGFR-mutant SCLC and neuroendocrine-differentiated LUAD successfully treated with osimertinib…SCLC cells were again positive for EGFR (Fig. 1F)…EGFR genotyping using a pleural fluid cell block identified an identical Del19. Treatment with osimertinib (80 mg/d) was initiated...osimertinib treatment was continued beyond progressive disease, with the pleural effusion remaining controlled for a total of 12 months from the initiation of the treatment (Fig. 2)....Combined assessment of EGFR mutation status and EGFR pathway activity would predict the efficacy of EGFR TKIs in patients with EGFR-mutated spontaneously transformed SCLC.