An experimental vaccine that is injected into melanomas can shrink them for an average of 8 months, according to findings presented at the American Society of Clinical Oncology’s 2013 meeting. Called talimogene laherparepvec (T-VEC), this immunotherapy consists of a virus engineered to carry human genes for granulocyte macrophage colony-stimulating growth factor (GM-CSF). Once inside a tumor, T-VEC kills tumor cells both by bursting them and by boosting the immune response against them. In a phase III clinical trial, melanomas shrank in 16% of those injected with T-VEC (48 out of 295) compared to just 2% of those treated directly with GM-CSF (30 out of 141). Moreover, melanomas disappeared completely in more than 10% of those treated with T-VEC. Doctors caution that because T-VEC is injected into melanomas, this treatment is only practical for people with accessible tumors.