As Charles Darwin famously stated, “[it] is not the strongest of the species that survives, nor the most intelligent, but the one most responsive to change.” This philosophy not only applies to animals in an ecosystem – but also to tumors. Extensive research conducted by scientists from the Cancer Research UK’s London Research Institute suggests that tumors evolve as they grow. Further, no two samples from the same tumor are identical – even those from adjacent regions. The findings of the study published in The New England Journal of Medicine in March may represent a major breakthrough in our understanding of tumor biology.