Another research interest in Orkin’s lab is osteosarcoma, the most common form of bone tumor. It usually occurs in adolescents, many of whom already have metastases to the lung by the time they seek medical care, making this condition highly lethal and very difficult to treat. Orkin and colleagues have modeled osteosarcoma in mice by inactivating two genes in immature progenitor cells before they differentiate into bone cells. The team is now investigating the genes involved in the progression of this tumor and hopes to find compounds that will push the immature cancer cells into a more differentiated state. At left: Osteosarcoma in the mouse, affecting the left limb.