clonal evolution

Clonal evolution is natural selection playing out inside a tumor, generation after generation of dividing cells. Picture a population of cells competing for room and resources, where any cell that happens to gain a useful mutation leaves more descendants. Over time the tumor becomes dominated by the lineages that grow best, just as advantageous traits spread in a population of organisms.

A clone is the set of cells descended from a single ancestor. As a tumor grows, random mutations create new variants; those that confer a growth or survival advantage are favored by selection and expand, while others stay rare or die out. The result is a tumor that is genetically diverse, a patchwork of related but distinct subclones.

This process explains why cancers can progress, spread, and develop resistance to treatment: a therapy may kill most cells, yet a rare subclone carrying a resistant mutation can survive and regrow. Clonal evolution links cancer biology directly to the principles of mutation and selection that drive evolution everywhere.