**4. Future prospective**

As I have described here, several common transcription factors are involved in the regulation of ES cell self-renewal and cancer cell growth (Fig. 2). This raises several intriguing possibilities. Considering that these common transcription factors are stem cell-specific and are involved in tumor growth, it is possible that they are specifically expressed in cancer stem cells and play important roles in the growth of these cells. Therefore, it is possible that these factors are good markers of cancer stem cells. If so, it might be possible to utilize these factors to isolate cancer stem cells, which will help to advance cancer stem cell research. Furthermore, identification of small compounds that specifically inhibit the functions of these factors may lead to the development of new anti-cancer drugs that can selectively kill cancer stem cells.

Since ES cells and iPS cells have similar gene expression profiles, it is likely that these common transcription factors are also expressed in iPS cells. Considering the transforming potential of these factors, it is possible that their high expression in iPS cells increases the risk of tumor formation during cell therapy using iPS-derived cells. Indeed, we have already found that *Zfp57*-null ES cells are significantly less able to form tumors than wild-type ES cells.

In this way, understanding the roles of putative oncogenes in ES cells will not only help to elucidate the molecular basis underlying the similarity between ES cells and cancers cells, but will also help to develop a novel method that can be used in cancer therapy and regenerative medicine.

**Figure 2.** Transcription factor network that regulates ES cell self-renewal. Considering the similarities between ES cells and cancer cells, at least a part of this network may be used for growth regulation in cancer cells.
