The importance of epigenetic changes in driving tumour progression is well established, but whether epigenetic alterations alone can initiate malignancy has been unclear. Parreno, Loubiere et al. now show that in Drosophila, a transient epigenetic perturbation can induce tumour formation.

Comparison of transcriptomes and hierarchical clustering of controls, constant and transient ph-knockdown tumours revealed genes that are reversibly or irreversibly altered following PH restoration. Genes enriched among irreversible genes included Janus kinase (JAK)–signal transducer and activator of transcription (STAT) ligands and downstream signalling effectors (for example, zfh1).