Cancer is an evolutionary disease. The same forces that turned dinosaurs into birds turn normal cells into cancer: genetic mutations and traits that confer a survival advantage.
Evolution in animals is largely driven by mutations in the DNA of germ cells – the sperm and egg that fuse to form an embryo. These mutations may confer traits that differ from those of the offspring’s parents such as larger paws, sharper teeth or lighter hair color. If the change is beneficial, like a mutation that lightens the hair of a rabbit living in a snowy climate, the animal is better able to survive, mate and pass on its mutated gene to the next generation. Such changes accumulate over millions of years, eventually turning, for example, dinosaurs into bluebirds.
Evolution is natural selection of particularly advantageous traits over time.
Cancer arises by these same evolutionary pressures, but at the level of individual cells within a person’s body. Instead of animals fighting for survival in a harsh environment, cells compete for space and nutrients. Because different organs are composed of different kinds of cells, cancers arising from different organs differ from one another in appearance and behavior and in how well they respond to treatment.
We are a team of oncologists, pathologists and translational scientists who work together to study how cancers evolve. We believe that understanding evolution is key to understanding how cancer arises and how to treat it.
Timing is of the essence
Human cells are normally in a constant state of death and renewal. Old cells die and are replaced by new ones. These phases of death and renewal are usually orderly, with cells cooperating in a complex process that provides them with proper nutrition and replaces them at a constant rate, maximizing the overall function of the organ they make up.
Mutations disrupt this orderly process. Changes to the cell’s DNA alter the proteins that comprise the cell’s structure and govern its behavior, sometimes in ways that lead it to duplicate itself faster than its neighbors, resist normal death signals and sequester nutrients for itself.
The immune system attacks and kills mutant cells in most cases. However, if one survives and duplicates itself many times over, it can form a tumor made of multiple mutant cells. These tumor cells continue to reproduce and mutate, evolving until the tumor ultimately gains the ability to spread throughout the body.
This microscopy image shows precancerous pancreatic tissue in mice.
Nathan Krah, University of Utah, CC BY-NC
Cancer detected at the earliest stages of this evolution can be treated more effectively than cancer at more advanced stages. This observation underlies the effectiveness of cancer screening programs in reducing cancer rates.
For example, colon cancer begins as a polyp, a small tumor on the interior…