The decision represents a victory for cancer patients, researchers and geneticists who claimed that a single company’s patent raised costs, restricted research and sometimes forced women to have breasts or ovaries removed without sufficient facts or second opinions.

But the court held out a lifeline to Myriad Genetics, the company with an exclusive patent on the isolated form of genes that can foretell an increased genetic risk of cancer. The justices said it can patent a type of DNA that goes beyond extracting the genes from the body.

Justice Clarence Thomas wrote the decision for a unanimous court. “Myriad did not create anything,” Thomas said. “To be sure, it found an important and useful gene, but separating that gene from its surrounding genetic material is not an act of invention.”