Flow cytometric analysis of DNA ploidy level in fresh tissue samples of human breast tumors has been carried out extensively. Recently, investigations regarding the prognostic value of nuclear DNA content have been facilitated by using nuclei isolated from paraffin-embedded tissues. The aim of our study was to monitor the possible differences between the analysis in fresh and fixed paraffin-embedded tissues in the same tumor and to investigate the possible prognostic implications obtained with this new approach. Nuclei suspensions were obtained, according to the method proposed by Hedley et al. with minor modifications, from 45 carcinomas and 5 fibroadenomas. Flow cytometric analysis revealed diploidy in 57% of carcinomas, while the remaining 43% showed cytometric aneuploidy. Corresponding results were observed between fresh and paraffin-embedded tissue in 26/35 cases. Moreover, a fairly good correlation between the DNA indices of fresh and paraffin-embedded carcinoma samples was observed. Furthermore, the frequency of recurrence was higher in the aneuploid group. Finally, 4 fibroadenomas were diploid and one was aneuploid. Our results confirm that this approach permits retrospective studies to evaluate the potential prognostic significance of nuclear DNA content monitored by flow cytometry.

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