[Sarcoma 180: growth and regression. Comparative investigations using flow-through and scanning cytophotometers as well as histological, cytological and autoradiographic techniques (author's transl)].

Material and methods: The growth and the regression of the experimental tumor S 180 was investiaged by volume measurements and by cytophotometric studies on 50 mice in each of a pilot and in the present main experiment. In addition, histological, cytological and cytokinetic examinations were performed.

Results and discussion: Beginning on day 18, a spontaneous regression of the tumor was found in 20% and 38% of the animals, respectively. DNA-measurements were performed with a scanning-microspectrophotometer on tumor tissue imprints and tumor cell suspensions and were also carried out with a flow-through cytophotometer ICP on suspensions. DNA-histograms were plotted on days 4, 7, 12, 18, 20, 22, 26 and 29 after the transplantation. These revealed a constant position of the maxima at 2C for normal cells and at 4C and 8C for the tumor cells. In particular, by measuring a large total number of 4,968,000 nuclei with the ICP, distinct changes were found in the proportion of the single nuclei classes during growth and spontaneous regression. This technique also enables a quantitative measurement to be made of the DNA of cell debris from necrosis. With growing tumos, the proportion of the tumor cells increased to a maximum of 65% on day 18 and decreased to 37% on day 29. The DNA of cell debris grew from 8% to 47%. The proportion of normal cells was only 10% to 15% in the final phases. In tumors with a spontaneous regression the proportion of the tumor cell nuclei was 20% on day 18 and 11% on day 29. The proportion of the DNA of cell debris was again about 45%. The proportion of normal nuclei was greatly increased to 45%. Histological and cytological evidence together with measurements of the areas of nuclei and incorporation of 3H-TdR confirmed that the normal cells, the number of which increased during spontaneous regression were cells of a fibrovascular granulation tissue. While the rate of the DNA-synthesis of growing tumors continously decreased with age there was also a rapid decrease of the labelling index of spontaneously regressing tumors between days 12 and 18. In the final phase only the nuclei of the granulation tissue were labelled.