A simple method to select specific tumor areas in paraffin blocks for cytometry using incident fluorescence microscopy.

A simple method is described for the selection of tumor areas in paraffin blocks for cytometry. The surface of a paraffin block is stained with the fluorescent dye DAPI. By means of incident fluorescence microscopy on the cut surface of a total block, the tissue can be visualized. Location of the tumor area with the aid of conventional histopathological criteria is feasible using the adjacent section after hematoxylin-eosin staining as a diagnostic guideline. Once the position of the tumor area is determined, a small hollow bore, which is screwed in the objective holder, is pressed in the tissue. The depth is controlled by the microscrew of the microscope. After retraction of the bore, the block is removed, and a thick section is cut. The selected area can be processed for cytometry separately from the remaining tissue. The technique can be used either to enrich the sample to be analyzed with tumor cells or to analyze histopathologically different tumor compartments. Both flow and image cytometry can make use of this selection technique.