Systemic Chemotherapy in Patients with Synchronous Peritoneal Metastasis from Gastric and Esophagogastric Junction Cancers Has No Uniform Effect on the Peritoneal Cancer Index

Abstract Background The prognosis of patients with peritoneal metastasis (PM) from gastric cancer or adenocarcinoma of the esophagogastric junction (EGJ) remains poor. Diagnostic laparoscopy plays a key role in evaluating the extent of PM, facilitating accurate Peritoneal Cancer Index (PCI) assessment. However, the extent to which systemic therapy alters the PCI and whether such changes are reflected in PCI dynamics remains insufficiently understood. This study aimed to evaluate the effect of systemic therapy on the PCI in patients with synchronous PM and to identify clinical and pathological factors associated with PCI development. Patients and Methods In this retrospective analysis, 69 patients undergoing laparoscopic or open surgical exploration for PCI assessment prior to and following systemic treatment were evaluated. The primary outcome measure was the binary outcomes of decrease and increase of the PCI, and the influence of age, sex, tumor grading, presence of signet ring cells, type of systemic treatment, and tumor localization was analyzed. Results The PCI was higher in 56.5% of patients and stable or lower in 43.5%. High tumor grading (G3) was significantly associated with increasing PCI values ( p = 0.002) despite systemic treatment. No statistically significant effects were observed for sex, age, signet ring cells, or tumor localization although estimated odds ratios using multiple regression analysis may suggest the presence of potential associations. Conclusions Laparoscopy is essential for the assessment of peritoneal tumor burden. There is no uniform macroscopic response of PM to systemic therapy. Tumor grading might represent a relevant prognostic factor for PCI response to systemic therapy, which should be addressed in future investigations.