# Gastric Cancer Peritoneal Staging: Progress and Persistent Challenges

## TL;DR

Staging laparoscopy and peritoneal lavage are key for gastric cancer, but differences in how labs interpret results remain a challenge.

## Contribution

The paper highlights the need for standardized pathology practices and molecular tools to reduce variability in peritoneal lavage cytology.

## Key findings

- There is broad consensus on performing staging laparoscopy and peritoneal lavage in gastric cancer.
- Pathology labs show significant variability in interpreting lavage cytology, leading to inconsistent results.
- Diagnostic inconsistency may affect treatment decisions for emerging therapies like NIPS and PIPAC.

## Abstract

Staging laparoscopy with peritoneal lavage has become a cornerstone of gastric cancer staging, particularly for identifying occult peritoneal disease. Recent Dutch and European Delphi consensus studies have now established broad agreement on indications for staging laparoscopy, systematic peritoneal inspection, and technical aspects of peritoneal lavage. However, while consensus on how to perform the procedure has advanced substantially, there remains striking heterogeneity in how peritoneal lavage cytology specimens are handled and interpreted by pathology laboratories. A recent multicenter Japanese survey demonstrated more than a tenfold variation in cytology positivity rates across high-volume centres, closely associated with differences in laboratory methodology. Similar variability has been acknowledged in European centres but remains largely unquantified. This diagnostic inconsistency has become increasingly consequential as novel treatment strategies for cytology-positive and low-volume peritoneal disease, such as Normothermic Intraperitoneal and Systemic chemotherapy (NIPS), cytoreductive surgery with HIPEC, and pressurised intraperitoneal aerosol chemotherapy (PIPAC), enter clinical practice. Failure to address cytological heterogeneity risks misclassification, inappropriate treatment allocation, and inequitable access to emerging therapies. Future efforts should focus on extending consensus into the pathology laboratory and exploring molecular adjuncts, including peritoneal cell-free DNA, to reduce diagnostic variability.