[Problems in DNA ploidy analysis using flow cytometry--influences from contaminant mononuclear cells]

The present study was undertaken to examine the influences of excessive contamination by lymphocytes on the flow cytometric analysis of DNA ploidy of head and neck cancers. Although lymphocytes which contaminate test cells can serve as an internal control (2C), an excess of these lymphocytes can mask the aneuploid peak of cancers. This tendency was particularly prevalent in well-differentiated squamous cell carcinoma. In some cases, most of the cells isolated from tumor-positive HE-stained tissue samples were lymphocytes. This is probably because lymphocytes are likely to survive the cell-isolating procedure, whereas keratocytes are likely to be destroyed during it. If samples excessively contaminated by lymphocytes are subjected to flow cytometry, the aneuploid peak of cancer cells is low relative to the 2C peak, possibly causing an erroneous judgment of diploid. Cytofluorometry, in which a smear of test cells is observed directly to quantify the DNA of cancer cells alone, was useful in detecting lymphocyte-masked aneuploid cells.