Growth dependent cell proliferation kinetics of a human malignant melanoma grown in nude mice

A human malignant melanoma was grown in nude mice. The tumour showed an exponential growth for several weeks which gradually slowed down, until following week 8 the tumour growth ceased. The reasons for this growth pattern were examined by labelling techniques (PLM, LI). The tumour cell production as quantified by the growth fraction, showed only a moderate reduction which, taken alone, could not explain the growth cessation. The important mechanism seems to be an increased loss of tumour cells during the intermitotic interval. While the loss of cells/h remains constant the total intermitotic cell loss is increased because the cell cycle times are prolonged by 50% from the exponential phase (45 h in week 3) to the plateau phase (66 h in week 8).