Flow cytometric DNA analysis of breast cancer by two colour method using cytokeratin labeling for identification of tumour cells.

Flow cytometric assessment of DNA-ploidy and S-phase fraction in breast cancer is compromised by the heterogeneity of cell subpopulations derived from the malignant and surrounding connective tissue, e.g. tumour, stromal and inflammatory cells. To identify tumour cell subpopulations, epithelial cells were labeled by a FITC-conjugated cytokeratin antibody (CK6, CK18) prior to flow cytometric cell cycle analysis in 205 fresh specimens of primary breast cancer. We found 158/205 (77%) DNA-aneuploid tumours compared to 127/205 (62%) without identification of cytokeratin positive cells (P < 0.001). In addition, the number of detected DNA-multiploid tumours rose from 31 (15%) to 51 (25%) after gating for cytokeratin positive cells. In DNA-diploid tumours, S-phase and G2M-phase fractions were significantly higher in cytokeratin positive (tumour) cells compared to total cell populations (4.4% and 5.8% vs. 3.2% and 4.4%; P < 0.001). Cytokeratin negative cells were found in all tumours and can be used as internal standard for calculation of ploidy and for quality control (CV, linearity) of each individual sample. We conclude that at least 20% of DNA-aneuploid tumours would not have been diagnosed without cytokeratin labeling. In addition, influence of non-tumourous cell elements on cell cycle analysis can be markedly reduced. Therefore, both determination of DNA-ploidy and cell cycle analysis can be optimized by cytokeratin labeling.