TP53 and small cell lung carcinoma: TP53 is a common tumor‐suppressor gene and is more highly expressed in patients whose disease transforms to SCLC (82%), which is another factor for EGFR‐TKI resistance in lung adenocarcinoma.24 In our study, TP53 (6/12, 50%) was uniquely identified in CSF ctDNA, but there was no significant difference in disease control between patients with or without TP53. This result suggests that TP53 may play a role in the progression of LM, but larger sample size studies are required to further explore this possibility.