Figure 2.

Proliferating healthy cells in the bone marrow mutate at random times, possibly influenced by super-pharmacological doses of GCSF. As long as the cell population size is kept in check, genetic drift, and selection remove many of the mutants, whereas some mutants persist. When the population expands, new mutant clones become more easily established. At some point, a qualitative change in the proliferation rate occurs and the now malignant cell population starts rapidly expanding.