[DNA flow cytometry. Comparison of the methods for nuclear extraction from frozen and paraffin-embedded sections]

Cellular DNA content of solid tumors can be determined either from fresh, frozen, or formalin fixed, paraffin-embedded tissues. However, discordant results have been obtained using the paraffin-embedded technique, and lack of abnormal DNA stemlines in the paraffin-embedded as compared to either fresh or frozen tissues has been reported. In this study we evaluated the validity of nuclear extraction method from paraffin-embedded tissues, using 75 breast carcinomas whose DNA content was previously analyzed from frozen tissue and resulted either normal (12 cases) or abnormal (63 cases). From representative paraffin blocks, nuclei were extracted following Hedley's technique. The results revealed excellent cell counting and good histogram resolution from all paraffin samples; the loss of G2M abnormal peak in eight histograms with abnormal stemline did not compromise the correct interpretation of DNA content. In addition, the comparison between DNA indices obtained from corresponding paraffin and frozen samples showed a good correlation in 69 cases (r = 94); discordance in six cases was demonstrated to be related to tumor heterogeneity. In conclusion the paraffin extraction method is a sensible, and reliable technique, which can be applied for DNA flow cytometric studies on archival cases, as well as whenever fresh sample from the tumor is not obtainable.