Cytoreductive surgery plus hyperthermic intraperitoneal chemotherapy versus R0 resection for resectable colorectal cancer with peritoneal metastases and low peritoneal cancer index scores: A collaborative observational study from Korea and Japan

Background: The benefits of hyperthermic intraperitoneal chemotherapy (HIPEC) after cytoreductive surgery (CRS) for colorectal cancer with peritoneal metastasis (CPM) remain controversial. R0 resection without peritoneal stripping might be as effective as CRS plus HIPEC. We aimed to compare the long-term oncological outcomes of patients with CPM and peritoneal cancer index (PCI) scores ≤6 who underwent R0 resection in Japan with those who underwent CRS plus HIPEC in Korea. Materials and Methods: This international, retrospective cohort study was conducted in Korea and Japan using a prospectively collected clinical database. Patients who underwent surgery from July 2014 to December 2021 for CPM with a PCI score of ≤6 and completeness of the cytoreduction score-0 were included. The primary outcome was relapse-free survival (RFS), and the secondary outcomes were overall survival (OS), peritoneal RFS (PRFS), and postoperative outcomes. Results: The 3-year RFS was significantly longer in the CRS+HIPEC group than in the R0 resection group: 35.9% versus 6.9% ( P<0.001 ); 31.0% versus 6.7% ( P=0.040 ) after propensity score matching. The median PRFS was significantly longer in the CRS+HIPEC group than in the R0 resection group: 24.5 months versus 17.2 months ( P=0.017 ). The 3-year OS and postoperative complications did not significantly differ between the two groups. Conclusions: RFS and PRFS rates were significantly prolonged after CRS plus HIPEC, whereas postoperative complications and length of hospital stay were not increased. Therefore, curative CRS plus HIPEC may be considered a treatment strategy for selected patients with resectable CPM and low PCI scores.