Seriate cytology vs molecular analysis of peritoneal washing to improve gastric cancer cells detection.

Background: Intraperitoneal malignant cells detection in patients with gastric cancer is associated with a significant decrease in overall survival. The overall accuracy of cytological examination of peritoneal lavages, however, is quite low, and intraperitoneal recurrence has been observed even in patients with negative cytology. Immunocytochemistry and molecular techniques have been investigated to improve high-risk patients' identification with variable results. The aim of this study was to compare the performance of different laboratory methods applied to peritoneal washing, to improve the cytological identification of malignant cells.

Methods: We prospectively evaluated 21 patients who underwent surgery and peritoneal lavage for gastric cancer. Among them, 18 had negative cytology and three were positive for malignant cells. For each patient, immunohistochemistry with BerEP4 antibody was performed on seriate sections of cellblock preparation at different levels, using the method reported for sentinel nodes in other types of cancer. Paired frozen quotes of washing fluids were evaluated by qRT-PCR with primer for mRNA of Ceacam5.

Results: In 4 of 18 patients with previous negative routine cytology, isolated neoplastic cells in seriate sections of the cellblock inclusion have been found. Results showed to be coherent with molecular analysis for CEA mRNA.

Conclusion: The sensitivity and specificity of peritoneal washing analyses should be notably improved by immunohistochemistry applied to multilevel cellblock sectioning. The method is less expensive and more widely applicable than molecular analysis, in each laboratory setting. This approach allows detection of minimum peritoneal seeding in patients with gastric cancer.