Malignant pleural disease is highly associated with subsequent peritoneal metastasis in patients with stage IV non-small cell lung cancer independent of oncogene status

Introduction: Peritoneal metastasis from lung cancer is an uncommon clinical event and there are limited data on what factors predict peritoneal progression. This study retrospectively investigated whether patterns of metastatic spread and oncogene status in patients with advanced non-small cell lung cancer (NSCLC) are associated with peritoneal metastasis. Methods: Patients with metastatic non-squamous NSCLC (n = 410) were identified at the University of Colorado Cancer Center. Sites of metastatic disease and baseline oncogene status (EGFR, ALK, KRAS, or triple negative) were documented via a retrospective chart review. In patients with EGFR mutations who developed peritoneal disease, we documented the presence of known resistance mechanisms. Median time to peritoneal metastasis, time from peritoneal disease to death, and overall survival were collected. Results: Eight percent (33/410) patients in this study developed peritoneal metastasis. Malignant pleural disease at baseline was significantly associated with subsequent peritoneal spread. There was no association between oncogene status and peritoneal metastasis. Three patients with EGFR mutations who developed peritoneal metastasis had documented resistance to tyrosine kinase inhibitors (TKIs) in the ascitic fluid. Median time from stage IV disease to peritoneal metastasis was 16.5 months (range 0.6-108 months). There were no differences in overall survival between patients who developed peritoneal metastasis and those who did not. Conclusions: Malignant pleural disease is highly associated with peritoneal metastasis in patients with advanced NSCLC. The underlying mechanism is not clear. The presence of resistance mutations in ascitic fluid implies that poor drug penetration is unlikely to be the dominant mechanism. Despite being a late clinical finding, there were no differences in overall survival between patients who developed peritoneal metastasis and those who did not. Additional studies exploring treatment related factors in patients with malignant pleural disease that can reduce risk of peritoneal metastasis are warranted.