A quantitative evaluation of cytophotometric DNA analysis in retrospective studies using archival tumor specimens

Methods developed for the cytophotometric analysis of archival tumor specimens used in retrospective studies were evaluated quantitatively. May-Grünwald-Giemsa-stained cytologic slides up to 20 years old could be restained by the Feulgen reaction with excellent results if they were destained in methanol and refixed in formaldehyde prior to Feulgen staining. Storage time had only a minor influence on Feulgen stainability. However, a considerable variation in the intensity of the Feulgen stain was observed between different slides stained simultaneously; this variation was not related to storage time. As a consequence of this variation, the use of internal staining controls, such as granulocytes, is an absolute necessity in the quantitative comparison of different slides. By expressing DNA data from the tumor cells in relative values (c values) related to the internal staining control (with a defined mean value of 2c), Feulgen ploidy level determinations could be made as accurately from measurements on old, destained slides as on cells obtained from fresh tumor material. The ploidy level could also be accurately determined in most cases of prostatic carcinoma from measurements on histopathologic sections.