Abstract: Disclosed are methods of detecting and treating a cancer such as an ovarian cancer using stem cells. Detection methods include administering a plurality of labeled stem cells to a subject having, or suspected of having, a cancer; and detecting the distribution of the stem cells. In some configurations, the label can be a nanoparticle such as a mono-crystalline iron oxide, which can be detected by magnetic resonance imaging. Treatment methods include administering a plurality of stem cells comprising a therapeutic agent such as an enzyme which activates a prodrug. In some configurations, the stem cells harbor a nucleic acid sequence encoding a cytosine deaminase, the cells express the enzyme, and the treatment further includes administering the prodrug 5-fluorocytosine, which is converted by the cytosine deaminase to the cytotoxic metabolite, 5-fluorouracil (5-FU).