Detection of effusion tumor cells under different storage and processing conditions.

Background: Circulating tumor cells (CTCs) shed into blood provide prognostic and/or predictive information. Previously, the authors established an assay to detect carcinoma cells from pleural fluid, termed effusion tumor cells (ETCs), by employing an immunofluorescence-based CTC-identification platform (RareCyte) on air-dried unstained ThinPrep (TP) slides. To facilitate clinical integration, they evaluated different slide processing and storage conditions, hypothesizing that alternative comparable conditions for ETC detection exist.

Methods: The authors enumerated ETCs on RareCyte, using morphology and mean fluorescence intensity (MFI) cutoffs of >100 arbitrary units (a.u.) for epithelial cellular adhesion molecule (EpCAM) and <100 a.u. for CD45. They analyzed malignant pleural fluid from three patients under seven processing and/or staining conditions, three patients after short-term storage under three conditions, and seven samples following long-term storage at -80°C. MFI values of 4',6-diamidino-2-phenylindol, cytokeratin, CD45, and EpCAM were compared.

Results: ETCs were detected in all conditions. Among the different processing conditions tested, the ethanol-fixed, unstained TP was most similar to the previously established air-dried, unstained TP protocol. All smears and Pap-stained TPs had significantly different marker MFIs from the established condition. After short-term storage, the established condition showed comparable results, but ethanol-fixed and Pap-stained slides showed significant differences. ETCs were detectable after long-term storage at -80°C in comparable numbers to freshly prepared slides, but most marker MFIs were significantly different.

Conclusions: It is possible to detect ETCs under different processing and storage conditions, lending promise to the application of this method in broader settings. Because of decreased immunofluorescence-signature distinctions between cells, morphology may need to play a larger role.