Peripheral blood mononuclear cells are a reliable internal standard for the flow cytometric DNA analysis of frozen malignant breast biopsies.

DNA ploidy and S-phase estimations are widely used as prognostic indicators in treatment decisions for breast cancer patients. For accurate calculation of the DNA index there is a need to identify the G0G1 diploid peak position. This study tested the reliability of peripheral blood mononuclear cells (PBMCs) as a diploid internal standard in the flow cytometric DNA analysis of 60 frozen malignant breast tumors. For each tumor, PBMCs were added to a duplicate sample prior to staining. There were 55 tumors with interpretable histograms; 18 were DNA diploid, 37 were DNA aneuploid, and all tumors had coefficients of variation < 5.0%. For each of the 55 tumors, whether diploid or aneuploid, the addition of PBMCs gave a unimodal peak at the diploid peak position. The results show that PBMCs are a reliable standard to identify the G0G1 diploid peak position.