To investigate further the contribution of adaptive immune responses to the anti-cancer activity of ingenol mebutate, B16 tumours were grown subcutaneously to 10–20 mm2 in Rag1-/- mice (C57BL/6 background), which are unable to generate adaptive B or T cell responses, and in control C57BL/6 mice. This evidence concerns the gene RAG1 and neoplasm.