Early effects of preoperative irradiation upon the cell cycle composition in rectal adenocarcinomas. A flow-cytometric DNA investigation.

The DNA patterns were studied by means of flow cytometric analysis in 43 rectal adenocarcinomas. Ploidy level and cell cycle distribution were related to clinical stage and histopathology. The frequency of grossly aneuploid tumours and tumours with multiple aneuploid cell populations increased with more advanced clinical stages and with the degree of dedifferentiation. In 15 cases the DNA pattern was studied before and after preoperative irradiation. The ploidy level was not affected by irradiation. A pronounced increase in the proportion of G2 cells was found after irradiation. This G2 blockage was proportional to the amount of S-phase cells before irradiation. Since following irradiation the proportion of S-phase cells was low and the proportion of G1 cells unchanged, the existence of a high fraction of resting G1 tumour cells can be assumed.