Cancer is the leading cause of death in economically developed countries, and in the United States alone, over half a million people lose their lives to this disease- with overall costs estimated to be upwards of $225 billion, each year. Studies have shown that the capacity of tumors to grow is due to a special type of cell, the cancer stem cell. Normal stem cells and cancer stem cells have much in common, such as the ability to self-renew, however genes believed to be involved in these processes are poorly characterized and little is known about their mechanism of action. The freshwater planarian Schmidtea mediterranea is unique in the sense that it is chalk full of stem cells! This confers amazing regenerative abilities, such as being able to regenerate an entire animal from a fragment smaller than 1/250th. Additionally, powerful experimental techniques have been developed to study stem cell biology in a detailed way, making this an ideal model system to study stem cell behaviour. I predict that key molecular systems that regulate stem cell biology have been preserved through evolution, and are thus necessary for stem cell survival in both planarians and cancer stem cells. Our lab has recently identified a collection of common genes (over 100) that underlies stem cell biology in planarians, mice and humans. Preliminary data suggests these genes are critical for the survival of stem cells, and for normal stem cell behaviour. I will complete these genetics screens and characterize the effect of each gene on the stem cell population in planarians. Genes found to be harmful to stem cell health will then be studied in cancer stem cells to discover how essential they are for the survival of cancer stem cells. Altogether, my work will provide valuable insight into stem cell biology and identify novel target genes for the development of therapies targeting cancer stem cells.