PTEN and melanoma: Here we clarify the cellular complexity of melanoma during early stages of tumor development by focusing on two mouse models of “minimal” induction in which melanocytes are engineered to express only activated Braf, or activated Braf plus a single null allele of the tumor suppressor Pten. On a genetic background that allowed for rare melanoma emergence even when only Braf was mutated, the kinetics of tumor appearance were consistent with a requirement for a single stochastic event.