p53 expression measured by flow cytometry. A comparison of three monoclonal antibodies and the relationship with grade and DNA ploidy in breast cancer.

The aim of this study was to quantify p53 expression by flow cytometry. A panel of three monoclonal antibodies: NCL-p53-240, NCL-p53-1801 and NCL-p53-DO7, was tested on breast cell lines and primary breast cancers. The relationships between ploidy, tumour grade and p53 expression for each antibody, were examined. Methodology was assessed using a variety of breast cell lines. Staining patterns were confirmed and the quantification technique qualified. Cytokeratin-positive cells from 58 samples obtained from patients with breast cancer were assayed for DNA content and p53 expression. p53 quantification was performed using calibrated fluorescent beads on cytokeratin-positive cells. Bloom and Richardson grading revealed 20 grade I and 38 grade II/III breast cancers. Examination of fluorescence thresholds showed a positive correlation between grade and DO7 (P = 0.003) at a level of 8900 molecules, 240 (P = 0.005) at a level of 2900 molecules and 1801 (P = 0.005) at a level of 1850 molecules. These levels equated with 34% (DO7), 43% (240) and 43% (1801) of the samples being classified as p53-positive. Examination of ploidy revealed 23 diploid and 35 aneuploid breast cancers. Application of p53 threshold levels on diploid and aneuploid tumours showed correlation between aneuploidy and p53 expression for DO7 at a level of 9000 molecules, 240 at a level of 1900 molecules and 1801 at a level of 1800 molecules. These levels equated with 34% (DO7), 52% (240) and 52% (1801) of the samples being classified as p53-positive. We conclude that measurement of p53 by flow cytometry may be of clinical importance by indicating levels of positivity using fluorescence thresholds. p53 expression has been shown to correlate with both grade and ploidy. Flow-cytometric measurement of p53 may be a useful prognostic assay.