Simulating the dynamics of primary seeding. (a) The total tumour burden for three different conditions where the removal rate was fixed at λ = 10−5 and return probability was taken to be p = 10−2, 10−3 and 10−4, respectively. (b) Illustrates the model dynamics when the parameters λ and p are varied systematically, and shows that accelerated tumour growth only occurs for large values of the leaving rate λ and the return probability p. The parameter regions corresponding to primary and secondary seeding are encircled in the figure, and the error bars show the estimated error in the Fermi estimate. These results suggest that only secondary seeding has the capability of accelerating tumour progression, whereas primary seeding occurs with rates that do not alter the rate of tumour progression. (Online version in colour.)