When we performed the same experiment in mice lacking adaptive immunity (RAG1−/− mice), we saw no significant difference in the growth of the contralateral tumour (221 mm2 vs. 180.3 mm2 Figure 2h), confirming that a systemic factor derived from MEK1‐hi tumours exerts its anti‐tumour effect through adaptive immune cells. This evidence concerns the gene RAG1 and neoplasm.