Use of formalin fixed, paraffin embedded tumours for estimation of cellular DNA content and S-phase fraction by static cytofluorometry.

Sections with a thickness of 50 micron from 34 formalin fixed, and paraffin embedded tumours were deparaffinized and hydrated and the cells were disaggregated with pepsin. The cells were stained with Hoechst 33258 and a rapid method for static fluorometry was used. DNA ploidy and the fraction of cells in S-phase were estimated and compared with results obtained with freshly prepared cells. The coefficients of variation for the tumour stemlines for both the fresh and the embedded material were approximately 6 per cent. There was a good correlation between DNA ploidy determined from fresh and embedded material, respectively; there was also a close correlation between the fractions of S-phase cells estimated from fresh and embedded tumours. It was also possible to cut out small histologically defined lesions, such as carcinoma in situ of the breast from thick paraffin sections and obtain DNA histograms with high resolution.