Figure 1. Diagram for two simple models.

Variables x_i, 0 ≤ i ≤ n represent non-cancerous populations and y_i, 0 ≤ i ≤ n represent the cancer populations. The index indicates the level of instability. Parameters d_i represent death rates of populations x_i and y_i, parameters p_i represent instability induced mutation rates, μ, μ_i, 0 ≤ i ≤ n and ν_i, 0, ≤ i ≤ n represent mutations generating the unstable types. (a) Radial mutation network model. (b) Sequential mutation network model.