Flow cytometric DNA histograms of paraffin-embedded pheochromocytomas.

We proposed a new classification of pheochromocytomas according to DNA ploidy patterns. Proliferation index (PI = S% + 4C%) might be an alternative to 4C% which was used as a critical marker of DNA nonaneuploid histograms. The follow-up survey revealed that DNA tetraploid with minimum increase of PI could not rule out the substantial possibility of malignancy and the comparison of DNA diploid histograms disclosed that 22 and 0% showed significant increase of the ratio of 4C% to S% under PI and 4C% criteria, respectively. In conclusion, 4C% was more effective and reliable than PI in order to classify DNA nonaneuploid pheochromocytomas.