Regional differences in surgical strategies for peritoneal metastases based on various perspectives on oligometastases

Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) has become a treatment option for peritoneal metastases (PM); however, it is not performed as widely in Asian countries, including Japan, as in Western countries. This regional disparity may be due to various perspectives on oligometastatic disease (OMD). In this review, we searched literature on surgical management for PM to investigate differential perspectives on OMD in each region. Gastric cancer: Two surgical strategies are employed: intraperitoneal chemotherapy (IPC) + gastrectomy in Asian countries and CRS/HIPEC in Western countries. The former requires the negative conversion of cytology and the disappearance of PM as indication criteria for surgery. The latter requires no progression. The IPC+gastrectomy strategy is based on induced OMD, and the CRS/HIPEC is on genuine OMD. Colorectal cancer: Japanese study groups recommend R0 resection for PM adjacent to the primary tumor or limited PM to the distant peritoneum. On the other hand, Western study groups recommend complete CRS for PM with a peritoneal cancer index ≤17. Historical investigations revealed that the strategy for R0 resection was based on the contiguous theory and that for CRS on the spectrum theory. Ovarian cancer: Surgical strategies do not differ markedly. However, the optimal surgery rate is markedly lower in randomized controlled trial from Japan than in others. Indications for radical surgery are more restrictive, and the roles of perioperative chemotherapy are more strongly emphasized in Japan than in Western countries because Japanese study groups are less likely to regard PM as OMD than Western study groups. Synopsis There are regional differences in the surgical management of peritoneal metastases between Japan and Western countries because Japanese study groups are less likely to regard PM as OMD than Western study groups.