Fig. 3: Minimal residual disease epitomizes the clinical challenge of heterogeneity and tumor plasticity.

a A small subpopulation of melanoma cells possess stem-like molecular and biological properties and undergo cellular proliferation at a slower rate than the rest (b, c) of the population. d Upon the addition of therapy (Rx), the bulk of the tumor is eliminated, except the stem-like subpopulation (minimal residual disease). e Under continuous therapy, the stem-like cells continue to proliferation and have the capacity to birth non-stem-like progeny. f Upon termination of therapy, the stem-like cells will again become scarce as the “normal” cycling cells continue to proliferate at a higher extent.