Fig. 1.

Variability in tumor progression. Number of cells with a given number of driver mutations versus the age of the tumor. Six different realizations of the same stochastic process with the same parameter values are shown, corresponding to tumor growth in six patients. The process is initiated with a single surviving founder cell with one driver mutation. The times at which subsequent driver mutations arose varied widely among patients. After initial stochastic fluctuations, each new mutant lineage grew exponentially. The overall dynamics of tumor growth are greatly affected by the random time of the appearance of new mutants with surviving lineages. Parameter values: mutation rate u = 3.4 × 10^-5, selective advantage s = 0.4%, and generation time T = 3 d.