Transcriptomics failed to reveal the expression of Hesx1, but stem cell markers such as SOX9, Klf2, Klf4 and Cmyc were upregulated in mouse tumours (J.R. Apps and J.P. Martinez-Barbera, manuscript submitted), sometimes in close proximity to the senescent cluster cells (i.e. SOX9; Fig. 4c)27. This evidence concerns the gene KLF4 and neoplasm.