Treatment Limitations and Missing Information in Peritoneal Metastatic Gastric Cancer

Background/Objectives: Peritoneal metastasis represents the most frequent and prognostically unfavorable metastatic pattern in gastric cancer, largely due to limited sensitivity of conventional imaging, delayed diagnosis, and insufficient response assessment. The aim of this review is to provide an overview of the current evidence on the diagnosis and treatment of gastric cancer with peritoneal metastases and to address current treatment limitations and options. Methods: This review was designed as a narrative review and is based on an extensive literature search in established databases. Results: Systemic chemotherapy remains the cornerstone of palliative treatment, improving the survival and quality of life compared with the best supportive care; however, outcomes in peritoneally metastatic disease remain poor. Advances in molecularly targeted and immune-based therapies have extended survival in selected patient populations, yet favorable molecular profiles are mainly unknown in peritoneal metastases. Staging laparoscopy and semi-quantitative assessment using the Peritoneal Cancer Index (PCI) are therefore essential for accurate diagnosis, prognostication, and treatment selection. Growing evidence from retrospective studies, multi-institutional cohorts, and selected randomized trials suggests that a multimodal approach—combining systemic therapy with intraperitoneal or bidirectional chemotherapy—may improve survival and quality of life. In carefully selected patients whose primary gastric tumor and peritoneal lesions respond to systemic treatment, complete cytoreductive surgery (CRS) followed by hyperthermic intraperitoneal chemotherapy (HIPEC) may further enhance outcomes and, in rare cases, achieve long-term survival. These potential benefits appear to be limited to highly selected patients with a low peritoneal tumor burden (PCI ≤ 6–7), positive cytology, good performance status, controlled extraperitoneal disease, and a high likelihood of achieving complete macroscopic cytoreduction (CC-0). Conclusions: Although the treatment intent in metastatic gastric cancer remains primarily palliative, carefully selected patients with limited peritoneal metastases may benefit from intensified multimodal treatment strategies when managed in specialized centers. Interdisciplinary evaluation, accurate staging, and individualized treatment planning are essential to optimize outcomes in this challenging disease setting.