Tumour cells use a genetic trick to become drug-resistant

Subscribe to enjoy similar stories.Cancers are real biological cheats. Whereas most of the cells in a healthy animal’s body get along by following the same set of genetic rules, cancer cells shamelessly ignore them.

Healthy cells, for example, can replicate themselves only about 50 times before shutting down. Cancer cells, by contrast, carry a mutation that allows them to divide indefinitely.

But recent work has revealed an entirely new level of oncological shenanigans. It now appears that many cancer cells have also stopped obeying Mendel’s laws of inheritance, explaining why many cancers are able to evolve resistance to chemotherapy drugs at seemingly supernatural rates.These laws, worked out in the 19th century by Gregor Mendel, an Augustinian friar, describe how heritable traits pass down through the generations, setting limits on the ways in which children can differ from their parents.

Mendel’s initial experiments were on peas in the monastery garden, but his laws have since been found to apply to everything from human height to disease resistance in individual cells.As Paul Mischel of Stanford University describes in a paper in this week’s Cell, some cancer cells refuse to play along. His work reveals that in about 20% of human cancer samples some DNA escapes from the chromosomes to which it is normally bound and forms tiny, circular bodies of extra-chromosomal DNA (ecDNA) that get scattered throughout the nucleus of a cell.

Thus scattered, they are no longer subject to the rigours of mitosis, the conventional process by which chromosomes divide into two identical copies, one for each daughter cell. This adds an element of unpredictability to how genes are inherited, allowing mutations to occur faster and on a