In some people with non-Hodgkin lymphoma (NHL), treating a single tumor with a mix of cancer therapies can help to shrink, or eliminate, tumors in other parts of the body, findings from a small clinical trial suggest. The approach is called an in situ vaccine because it uses something in the body (in situ)—in this case, an individual tumor—to help create a body-wide immune response. It’s currently being tested in a small clinical trial of patients with slow-growing, or indolent, subtypes of NHL. Initial results from the trial showed that delivering the treatment directly to a single tumor in a patient could create an immune response against, and shrink, tumors throughout the body. The findings were reported by Linda Hammerich, Ph.D., and Joshua Brody, M.D., of the Mount Sinai School of Medicine in New York, and their colleagues April 8 in Nature Medicine. In addition, experiments the research team performed in mice suggested that the vaccine may be even more effective when combined with an immune checkpoint inhibitor, a form of immunotherapy that is already used to treat Hodgkin lymphoma and many other cancers. As a result, the research team recently launched a second clinical trial to test the vaccine in combination with an immune checkpoint inhibitor. Last year, another group of researchers also reported positive results to treat indolent NHL, the most common subtype of which is follicular lymphoma. Although it’s still too early to say what will become of the vaccine used in this most recent trial, the approach “looks to be very promising,” said Benjamin Heyman, M.D., of the University of California, San Diego, whose research focuses on developing immunotherapies for lymphoma but who was not involved in the study. “This is certainly an important proof-of-concept finding,” agreed Wyndham Wilson, M.D., of NCI’s Center for Cancer Research, who also was not involved in the study. But whether the results seen in the trial participants will “turn out to be clinically meaningful will take more follow-up,” he cautioned.