In this issue of Oncogene, Serakinci et al show that adult stem cells can be targets for neoplastic transformation. After transducing human adult mesenchymal stem cells (hMSC) with the telomerase hTERT gene, and growing them for many population doublings in culture, Serakinci et al observed that the transduced cells developed characteristics consistent with transformation including loss of contact inhibition, anchorage independence and tumour formation in mice. Underlying these changes were alterations to genes involved in cell cycle regulation and senescence as well as oncogene activation. The importance of these observations is twofold. Firstly, showing that stem cells can become tumours raises a note of caution for stem cell therapeutics. Secondly, the findings lend support to the stem cell hypothesis of cancer development, and provide an experimental system in which the tantalizing hint of new diagnostic, prognostic, and therapeutic opportunities offered by this concept can be explored further.