Influence of systematic errors on the evaluation of the S phase portions from DNA distributions of solid tumors as shown for 328 breast carcinomas.

The portion of cells in S phase has proved to be a valuable prognostic indicator of early relapse and life expectancy, particularly in breast carcinoma. Comparisons of published data on samples of primary breast carcinoma biopsies showed that the values obtained by analyses of flow cytometric DNA distributions were generally higher than those of determinations based on the tritiated thymidine (3H-ThdR) labeling index (LI). Flow cytometric DNA analyses of 328 biopsy samples of primary breast carcinomas revealed that these differences could be explained by varying contributions of debris background. Since this influence is inversely proportional to the cell counts in each channel, it may cause considerable errors, particularly in the S phase channels, which normally contain the lowest counts of the DNA distributions. Two different mathematical rationales were tested in order to separate DNA distributions from the debris superimposition. No appreciable differences were found with respect to the essential results. After appropriate subtraction of the background levels, the previously reported discrepancies between cytometrically determined S phase portions and 3H-ThdR LI values disappeared, and good agreement was achieved for the comparable tumor samples of the present study. In conclusion, debris background subtractions should generally precede the DNA histogram analyses, particularly of solid tumors, in order to obtain reliable S phase values.