Ovarian cancer stem cells: elusive targets for chemotherapy

Ovarian cancer is one of the major causes of death in women with gynecologic malignancy. Most patients respond favorably to platinum therapy, but relapses are common. There is emerging evidence that a special subset of cells that is highly tumorigenic is responsible for recurrence of the disease. This subset of cells has been characterized by several groups and has been found to have the properties of cancer stem cells. They have been isolated from tumor samples obtained during surgical cytoreduction and also from the ascitic fluid of ovarian cancer patients. Currently, there are no known unique markers to define these cells, but several groups have used different approaches to purify them. Although some heterogeneity has been observed in these cells, most of them satisfy the functional definition of a stem cell. Advances in characterization of ovarian cancer stem cells are instrumental in developing therapies that specifically target them. This review describes the advances made in characterization of these cells, basis of their resistance to conventional chemotherapeutic agents and the prognostic implications of utilizing mechanisms specific to ovarian cancer stem cell for therapeutic interventions. Eliminating ovarian cancer stem cells could possibly lead to a prolongation of the disease-free survival period and hopefully a definitive cure.