An elite research group studied more than 1,500 advanced cancer patients who had undergone checkpoint-inhibitor immunotherapy. They uncovered that a mutational load of a tumor may be a potential way to predict a response to checkpoint-inhibitor immunotherapy across different forms of cancer. Checkpoint-inhibitor immunotherapy is a type of treatment for cancer patients where an attempt is made to prevent cancer cells from suppressing the body’s natural immune response—enabling it to fight off the tumor development. In some patients this works well; in others not so well. Researchers’ quest to identify which patients would benefit from such a treatment has led to a new effort where they found what they believe is a reliable way to test patients prior to administration of treatment—testing their mutational load. This refers to the tumor mutation burden, which is a number that describes the rate of DNA faults in a tumor. This is a way of quantifying mutation rates in tumors.