Peritoneal Lavage Cytology Following Neoadjuvant Chemotherapy for Gastric Adenocarcinoma: Low Yield in Detecting Peritoneal Metastases.

Background: Peritoneal lavage cytology (PLC) can detect advanced disease in gastric adenocarcinoma (GC); however, routine practice remains controversial. Furthermore, the effect of neoadjuvant chemotherapy (NAC) on cytological detection of carcinomatosis is unknown.

Methods: Using a 2012-2020 prospective database, we retrospectively reviewed patients with GC who underwent NAC followed by a staging laparoscopic peritoneal lavage with or without biopsy of suspicious peritoneal nodules. PLC results were considered discordant if they did not align with the peritoneal biopsy results. Patients with benign peritoneal cytology (Cyt-) or biopsy results who had postoperative time to carcinomatosis of <6 months were considered to have diagnostic failure of peritoneal lavage.

Results: Fifty-five patients with GC who underwent NAC followed by staging diagnostic laparoscopy with peritoneal lavage were identified. The majority of the patients in the cohort had Cyt- lavage (89.1%). Of the patients who underwent resection, 76.1% had T3 or greater disease on final pathology and 66% had nodal metastases. In 23 patients (41.8%) who had both peritoneal lavage and biopsy, four cases (17.4%) had discordant results. Diagnostic failure rate was 20% at 6 months and 42.2% at 12 months. The median time to carcinomatosis in patients who were Cyt- or biopsy negative was 7.9 months.

Conclusion: PLC after NAC has a high diagnostic failure rate and inaccurately predicts carcinomatosis in 20% of patients with GC. Novel methods for identifying cytology positive GC after NAC should also be developed and evaluated, since the risk of peritoneal dissemination is high.