The dynamics of evolution are fully in play within the environment of a tumor, according to a report in the December issue of the journal Nature Reviews Cancer. The report, from researchers at The Wistar Institute, could have profound implications for understanding why current cancer therapies often fail and how radically new therapies might be devised.
According to the study, there are three necessary and sufficient conditions for natural selection to occur and that all are met in a population of tumor cells. The first requirement is that there be variation in the population. This variation is evident in tumors, which are a mosaic of many different genetic mutants.
The second condition is that the variation must be heritable. This, too, can be seen within a tumor-cell population. When mutant tumor cells divide to replicate, the daughter cells share the same mutations.
The final condition is that the variation has to affect fitness, the survival and reproduction of the cells. All of the characteristics that are considered hallmarks of cancer affect fitness.
March 10, 2026 
