Peritoneal Oligometastasis in Gastric Cancer: Diagnostic Strategies, Patient Selection, and Emerging Therapeutic Approaches

Peritoneal metastasis (PM) from gastric cancer is a critical determinant of poor prognosis and has limited therapeutic options. However, recent advances in diagnostic and therapeutic strategies have reshaped the clinical landscape, enabling curative treatment of select patients. Accurate staging based on the peritoneal cancer index (PCI) is central to disease stratification and treatment planning. A PCI threshold of ≤6 has emerged as a consensus-based cutoff to define peritoneal oligometastasis, a limited metastatic state with potential for long-term survival following aggressive multimodal therapy. Therefore, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy remains the cornerstone of curative treatment. Additionally, innovative peritoneum-directed therapies—including normothermic intraperitoneal chemotherapy, early postoperative intraperitoneal chemotherapy, and pressurized intraperitoneal aerosol chemotherapy— have expanded the therapeutic landscape for both curative and palliative indications. This review highlights the evolving strategies for the diagnosis and treatment of gastric cancer with PM, with emphasis on PCI-based patient selection and treatment optimization. We also discuss the future roles of liquid biopsy, artificial intelligence, and photodynamic therapy in enhancing precision oncology for PM. Defining and targeting peritoneal oligometastases may enable tailored interventions and improve outcomes of this historically intractable disease.