Use of light scatter when recording a DNA histogram from paraffin-embedded tissue

The quality of a DNA histogram as recorded in a flow cytometer can often be improved by gating on forward and orthogonal light scatter. This may be helpful when measuring DNA histograms from formalin-fixed, paraffin-embedded material. We report that nuclei from many human tumours scatter more light orthogonally than those from normal stroma. Gating on light scatter enabled the DNA histogram from the tumour to be recorded with reduced contamination from normal cells. In studies of human mammary carcinomas, we have found that this method has the potential to improve the estimation of S phase and the measurement of DNA index (DI) when the DI is close to 1 (near diploid).