FGF9 and small cell lung carcinoma: Since the osimertinib-resistant cells increased the expression of an SCLC marker (synaptophysin), we speculate that HCC827 cells may use FGFR1 with FGF2 as well as FGF9 as alternative autocrine signals for cell survival in a DTP state, and resistant cells acquire resistance from the DTP state by MET amplification and maintain FGFR signal activation through FGFR1 upregulation.