Having an extra chromosome has a surprising effect on cancer

SAN FRANCISCO — Having an extra chromosome may suppress cancer, as long as things don’t get stressful, a new study suggests. The finding may help scientists unravel a paradox: Cells with extra chromosomes grow slower than cells with the usual two copies of each chromosome, but cancer cells, which grow quickly, often have additional chromosomes. Researchers have thought that perhaps extra chromosomes and cancer-causing mutations team up to produce tumors.

Jason Sheltzer, a cell biologist at Cold Spring Harbor Laboratory in New York, and colleagues examined the effect of having an extra chromosome in mouse cells that also have cancer-promoting mutations. Cells with an extra copy of a chromosome — known as trisomic cells — grew slower in lab dishes and formed smaller tumors in mice than cells with cancer mutations but no extra chromosomes. Even when trisomic cells carry cancer-associated genes on the extra chromosome, the cells make less than usual of the cancer-driving proteins produced from those genes, Sheltzer reported December 5 at the annual meeting of the American Society for Cell Biology.

Extra chromosomes aren’t entirely off the hook for promoting cancer, though. After cells carrying extra chromosomes were grown with a low dose of chemotherapy drugs, they grew faster than cells that don’t have extra chromosomes, Sheltzer discovered. That could be because cells remaining after chemotherapy have developed additional abnormalities that might make the cancer more aggressive, he said.