A novel combined fluorescent probe staining method for circulating tumor cell identification

Background: To develop a novel highly accurate circulating tumor cell (CTC) identification method and to validate its application in cancer diagnostics and/or prognostics. Methods: We verified and validated the combined fluorescent probe staining protocol (combination of three fluorescent probes: Dil, Hoechst 33342, and PY) through CTC and non-CTC (white blood cell) morphological comparison of five tumor cell lines (THP-1, HEC, HEPG2, Eca-109, HeLa) in vitro and 32 patient tumor samples from the Shandong Cancer Hospital and Institute. Wright's Giemsa staining and cluster differentiation 45 (CD45) immunocytochemistry (ICC) staining were used as reference control methods. The association between the developed method and clinicopathology was also investigated. Results: We successfully developed and optimized the protocol, and validated the use of combined fluorescent probe staining for the identification of CTCs in the peripheral blood (PB) of tumor cell lines and tumor patients. Comparable CTC and non-CTC morphologies were observed for combined fluorescent probe staining and Giemsa staining methods in vitro. However, in vivo comparison between the three staining methods revealed that the identified CTCs differed in cell diameter and nucleo-cytoplasmic ratio. In addition, a higher CTC detection rate of 14/32, lower standard deviation (SD), and higher area under the receiver operating characteristic (ROC) curve (AUC) value of 0.844 were noted for combined fluorescence staining. Clinicopathological analysis revealed that CTCs were correlated with platelet levels (P=0.031), but not with age, gender, drinking history, or granule ratio. Conclusions: We developed a combined fluorescent probe staining method with higher CTC identification accuracy than Wright's Giemsa staining, and propose this technique as a novel clinical diagnostic/prognostic tool.