A cancer-killing, virus-based therapy showed promising effects against retinoblastoma - a tumor of the retina that affects mainly children - in mouse models and a pilot clinical trial. Although further work is needed, the therapy lays the groundwork for new treatment options for the cancer, which is currently treated with disfiguring surgery. Researchers estimate that retinoblastoma causes 8,000 cases each year, a figure that represents 11% of all cancers in children under the age of one. Most cases result from inactivation of the gene RB1, which normally plays a critical role as a tumor suppressor. Chemotherapy is the standard-of-care for retinoblastoma, but intensive rounds of such drugs can damage the retina and cause long-term vision problems. In some cases, surgery is needed to remove the eye entirely - an invasive procedure called enucleation that results in loss of vision. Here, Guillem Pascual-Pasto and colleagues investigated an alternative treatment for retinoblastoma named VCN-01, which harnesses a virus that infects and kills cancer cells harboring a dysfunctional RB1 pathway. The treatment was safe in juvenile rabbit models, and injections of the virus into the eyes of mice with retinoblastoma (equivalent to a feasible dosage for human children) curtailed tumor growth, prevented metastasis, and extended the time to enucleation compared to chemotherapy. Importantly, the authors administered VCN-01 to two pediatric patients with retinoblastoma and observed the virus successfully replicated in tumor cells and did not cause systemic inflammation. Taken together, the findings warrant further development of VCN-01 as a potential treatment for patients with retinoblastoma and RB1 inactivation, Pascual-Pasto et al. say.