Via EurekAlert!, another demonstration of the use of existing cellular mechanisms as a part of cancer therapies: researchers "have been able to derive mesenchymal stem cells from human adipose, or fat, tissue and engineer them into 'suicide genes' that seek out and destroy tumors like tiny homing missiles. ... Mesenchymal stem cells help repair damaged tissue and organs by renewing injured cells. They are also found in the mass of normal cells that mix with cancer cells to make up a solid tumor. Researchers believe mesenchymal stem cells 'see' a tumor as a damaged organ and migrate to it, and so might be utilized as a 'vehicle' for treatment that can find both primary tumors and small metastases. ... the researchers worked to find a less toxic way to treat colon cancer than the standard-of-care chemotherapy agent, 5-fluorouracil (5-FU), which can produce toxic side effects in normal cells. They expanded the number of mesenchymal stem cells in the laboratory and then used a retrovirus vector to insert the gene cytosine deaminase into the cell. This gene can convert a less toxic drug, 5-fluorocytosine (5-FC), to 5-FU inside the stem cells, and the chemotherapy can then seep out into the tumor, producing a lethal by-stander effect. ... tumor growth was inhibited by up to 68.5 percent in the animals, and none of the mice exhibited any signs of toxic side effects."