Intensity of proliferation and sensitivity of experimental tumors to the 1-methyl-1-nitrosourea.

The kinetics of tumor growth and cell proliferation of eleven generations of spontaneous mammary carcinoma in F1(CBA2 X C57B1/6) mice was studied. Factors responsible for different sensitivity of tumors to 1-methyl-1-nitrosourea were analyzed. The process of tumor transplantation was accompanied by the reduction in latent period and the increase in the mean specific rate of tumor growth. The rise in tumor growth rate in consequent generations was associated with the increase of the number of DNA synthesizing cells. The fall in the intensity of the DNA synthesis was observed along with the tumor growth within one passage. The sensitivity of tumors to 1-methyl-1-nitrosourea was correlated reciprocally only with the initial labeling index of tumors and the specific rate of tumor growth.