Many people with an aggressive blood cancer called diffuse large B cell lymphoma are cured by the current gold standard of treatment: an antibody designed to wipe out cancerous B cells plus a combination of four chemotherapy drugs. However, this treatment regimen fails in about three in 10 patients, and its intense chemotherapy can cause heart damage—a serious risk for older patients, who make up a large share of those diagnosed.

Despite these risks, clinicians are often reluctant to try newer, potentially less-toxic treatment regimens, because there’s no reliable way to predict whether a patient’s cancer will respond.