Oncolytic virotherapy is a promising adjunct to conventional drug-based strategies for effective cancer therapies, and has progressed into late-phase clinical trials.3 An oncolytic herpes virus expressing GM-CSF has demonstrated higher response rates (26% vs. 6%) in malignant melanoma with durable clinical responses, lasting for a minimum of 6 months, in 16% of patients, compared with 2% in the control arm (GM-CSF treatment alone). Here, CSF2 is linked to cancer.