Pathological diaphragmatic invasion by colorectal liver metastases is associated with RAS mutation, peritoneal recurrence and worse survival.

Background: Risk factors for pathological diaphragmatic invasion from colorectal liver metastases (CRLM) and differences in recurrence patterns and survival between patients with true pathological diaphragmatic invasion versus inflammatory adhesions only remain poorly understood. This study aimed at identifying risk factors for and survival impact of pathological diaphragmatic invasion in patients with CRLM.

Methods: Patients with CRLM who underwent hepatectomy with or without diaphragmatic resection from 1998 to 2015 were retrospectively analyzed. Recurrence-free survival (RFS), overall survival (OS), and recurrence patterns were examined according to the presence or absence of pathological invasion.

Results: Of 1860 patients, 70 underwent hepatectomy with diaphragmatic resection and 1799 had hepatectomy only. Among the patients with gross diaphragmatic involvement, 15 (21%) had pathological invasion, and 55 (79%) had inflammatory adhesion only. Multiple tumors (p = 0.019) and RAS mutation (p = 0.047) were significantly associated with pathological invasion. Pathological invasion was associated with a higher incidence of peritoneal recurrence (33% vs. 11%, p = 0.041), worse median RFS (6 months vs. 11 months, p = 0.21) and OS (26 months vs. 51 months, p = 0.046) compared to inflammatory adhesion.

Conclusion: Multiple tumors and RAS mutant were predictors for pathological diaphragmatic invasion, which was associated with a higher incidence of peritoneal recurrence and worse OS.