Flow cytometry as the new ‘gold standard’ for detection of free tumour cells in abdominal lavage fluid in gastric cancer patients: A comparative study of molecular and conventional methods

Aim The ideal method for detection of free tumour cells in abdominal lavage fluid should be rapid, reliable and widely available. Flow cytometry potentially covers these properties, but there are only a few studies directly comparing flow cytometry for detecting gastric cancer cells to other methods. Therefore, we compared free tumour‐cell detection in abdominal lavage fluids using cytology with immunocytochemistry, RT‐qPCR and flow cytometry. Methods Peritoneal lavage fluid samples were collected from 10 patients. Detection of free tumour cells was performed using cytological and immunocytochemical analysis, and using RT‐qPCR and flow cytometry. Tumour cells were detected according to CEA and CK20 mRNA expression levels using RT‐qPCR , and with the epithelial markers EpCAM/CD326 and CEA using flow cytometry. Results The sensitivity and specificity of cytology were 40% and 100%, respectively, while the RT‐qPCR had a sensitivity of 80% and specificity of 100%. Flow cytometry showed no false‐negative results and only one false‐positive result, giving a sensitivity and specificity of 100% and 80%, respectively. The RT‐qPCR and flow cytometry could detect free tumour cells in each of the three false‐negative cases with cytology. In the samples with detected tumour cells, tumour cell clusters were observed with imaging flow cytometry, providing additional morphological confirmation. Conclusion The combination of quantitative and qualitative data from flow cytometry and the images of tumour cells in borderline cases provide a rapid, reliable and reproducible method for detection of free tumour cells in abdominal lavage fluid, which is necessary for intraoperative selection of patients for intraperitoneal chemotherapy.