DNA flow cytometry and histopathological grading of paraffin-embedded prostate biopsy specimens in a survival study

Methods to disintegrate old paraffin-embedded tissue blocks for the application of DNA flow cytometry open up new possibilities for retrospective studies on the correlation between tumor cell nuclear DNA pattern and prognosis of the neoplastic disease. In the present work we used such a method to study the relationship between DNA ploidy, histopathological grade, and survival for 50 patients with prostate carcinomas diagnosed 1958-1974. Plugs of histologically identified tissue from benign and tumor areas were sampled from paraffin blocks of prostate biopsy specimens by using a 4-mm skin biopsy punch. Thirty-micron sections were cut from each plug for dewaxing and disintegration. The cell suspensions obtained were stained with 4',6-diamidino-2-phenylindole dihydrochloride and analyzed by flow cytometry. In about one-half of the cases where two or more plugs were analyzed we found a heterogeneous tumor cell nuclear DNA pattern. No apparent correlation was found between the histopathological grade and the DNA ploidy. Using Cox's multiple regression analysis, we found a significant correlation between DNA ploidy and survival of these patients (P = 0.043) when we controlled for histopathological grade (Dhom grade), acid phosphatase level, occurrence of metastases, age, year of diagnosis, and type of biopsy. The correlation between DNA ploidy and survival was just above the level of significance (P = 0.059) when Gleason grade was substituted for Dhom grade in the regression model.