Trivariate flow cytometric analysis of paraffin‐embedded lung cancer specimens: Application of cytokeratin subtype specific antibodies to distinguish between differentiation pathways

The aim of the present study was to investigate whether trivariate FCM analysis, for the simultaneous detection of two different CK subtypes in combination with DNA content, can be applied to paraffin embedded samples of different types of non‐small cell lung cancer in order to evaluate the cell cycle of individual sublines. Single cell suspensions were prepared from 50 μm thick paraffin sections of 22 lung carcinomas by pepsin digestion and immunostained with CK‐antibodies which were chosen to distinguish glandular differentiation (adenocarcinomas) and squamous differentiation. There was a good correlation between the immunocytochemical results of the different CK antibodies in tissue sections and in the corresponding single cell suspensions. Gating for CK‐positivity revealed a higher S‐phase fraction as compared to the ungated cell population. The tumor cells in adenocarcinoma cases were specifically recognized by CK7 antibodies, while well‐differentiated squamous cell carcinomas were specifically stained for CK14 and/or CK17. In poorly differentiated squamous cell carcinomas simultaneous expression of CK7 and CK17 was detected in a subpopulation of the tumor cells, next to cells positive for CK7 or CK17 alone. The trivariate FCM analysis allowed the separate estimation of ploidy status and cell cycle parameters in the three different cell populations of these, apparently (phenotypically) heterogeneous, malignancies. Cytometry 27:179–188, 1997. © 1997 Wiley‐Liss, Inc.