With its ease of manipulation and expansive repertoire of available genetic tools, the vinegar fly Drosophila melanogaster has served a pioneering role in the study of cancer-causing genes and cooperative tumourigenesis.9, 10, 11 In Ras-driven epithelial overgrowth, studies in Drosophila have revealed that impairment of cell polarity or mitochondrial functions enhance tumour growth and invasion via activation of the Jun kinase (JNK) stress response pathway, faithfully recapitulating some of the features responsible for tumour progression in human cancers.11, 12, 13, 14, 15. Here, MAPK9 is linked to cancer.