Hand drawing from Athanasios N. Nikolakopoulos

Assuming that the primary tumor growth follows a multi-type branching process, the founder cell was the original type (type 0). A new type was born (type 1, which grows faster) as the tumor expands, which eventually reached a detectable fraction in the final tumor. Seeding from type-0 or type-1 would lead to distinct genomic divergence between the secondary tumor (originated from the seeding cell) and the primary tumor. The hand drawing above shows the transition in probability between seeding from type-0 and from type-1 cells as the primary grows. Let’s further posit that the seeding potential is somehow related to the fitness (growth rate) of a cell. The S-shape transition reflects that when enough of the type 1 are around in the primary tumor, the next division will come from this new type, which will devastate the probability of seeding from the type-0 cells.