First-line induction oxaliplatin-based chemotherapy followed by maintenance in isolated peritoneal metastatic colorectal cancer: Real-world outcomes from Vietnam.

Abstract

e15524 Background: Isolated peritoneal metastatic colorectal cancer (IPM-CRC) represents a rare and biologically unique entity characterized by poor survival. Although cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) has been explored, its survival benefit remains inconsistent, and systemic chemotherapy continues to represent the cornerstone of treatment. This population remains an underrepresented cohort in clinical research and is frequently pooled with other metastatic patterns, particularly in low- and middle-income settings where access to CRS/HIPEC is limited. We conducted this study to evaluate real-world outcomes of first-line induction oxaliplatin-based chemotherapy followed by maintenance therapy in patients with IPM-CRC. Methods: This ambispective, single-center cohort included 94 patients with IPM-CRC treated in Vietnam between 2019 and 2025. All patients received first-line oxaliplatin-based induction chemotherapy (CAPEOX or FOLFOX ± bevacizumab) and subsequently received maintenance therapy with capecitabine ± bevacizumab after 4–6 months of induction upon achieving partial response or stable disease. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan–Meier method. Response was evaluated using a dual approach: the objective response rate (ORR) per RECIST v1.1 in patients with measurable disease on imaging, and clinical benefit (symptom improvement or disease stabilization) in those without measurable lesions. The disease control rate (DCR) combined both measures. Adverse events (AEs) were graded per CTCAE v5.0. Results: The median age was 57 (range 18-78) years, with 72.3% male. Bevacizumab was administered in 79.8% of patients. With a median follow-up of 18.1 (95%CI 13.9-22.2) months, the median PFS and OS were 9.5 (95%CI 8.1-11) and 28.2 (95%CI 20.4-36.1) months, respectively. Among 55 patients evaluable for response assessment per RECIST v1.1, ORR was 32.9%. Across the full cohort, overall DCR was 75.5%; DCR was 78.7% among patients receiving bevacizumab and 63.2% among those treated without bevacizumab. The median duration of maintenance therapy was 7.9 (IQR 3.7-16.0) months. Grade 3–4 adverse events occurred in 13.8% of patients, most commonly neutropenia (11.7%). No treatment-related deaths were observed. Conclusions: This induction-to-maintenance approach demonstrates meaningful activity and feasibility in patients with IPM-CRC, even within a resource-limited setting. Continued analyses will help determine which patients benefit most.