Flow cytometric analysis of ploidy in solid neoplasms: comparison of fresh tissues with formalin-fixed paraffin-embedded specimens.

The DNA content of both fresh and formalin-fixed, paraffin-embedded tissues from 30 solid neoplasms was analyzed by flow cytometry. Cells from a single paraffin block of each tumor were disaggregated according to the method of Hedley et al. Cells were sampled from multiple sites of each fresh specimen. Fresh and deparaffinized cells were stored frozen and prepared for cytometric analysis by the technique of Vindelov et al. Thirteen fresh specimens showed DNA diploidy/tetraploidy and 17 showed DNA aneuploidy. Twenty-six of the 30 paraffin-embedded samples were concordant; aneuploid peaks present in histograms from fresh tissue specimens were absent in the 4 paraffin-embedded specimens that were discordant. For 2 of the discordant cases, a hyperdiploid peak that was absent in the initial paraffin-embedded samples was evident on analysis of cells from additional paraffin blocks, indicating ploidy heterogeneity. Peridiploid aneuploid peaks present in the other 2 fresh samples were not observed in initial or additional deparaffinized specimens. Although fresh tissues are preferred for ploidy examination by flow cytometry, formalin-fixed paraffin-embedded specimens, despite a few inherent pitfalls, are generally useful for retrospective studies that compare the ploidy status of solid neoplasms to therapeutic response and prognosis.