Now that scientists are well aware of cancer stem cells, it seems they are being found everywhere. From MedlinePlus: "Primitive cells that resemble stem cells may help some ovarian cancer tumors linger and recur in the body, but it may be possible to subdue them ... The findings build on other studies that show leukemia, breast, brain and other tumors have so-called side population cells that resemble the healthy stem cells found elsewhere in the body. ... Cancer stem cells, like somatic stem cells, are thought to be capable of unlimited self-renewal and proliferation ... The majority of patients who respond to primary chemotherapy ultimately develop recurrent, usually drug-resistant, disease that is conceivably due to the ability of ovarian cancer stem cells to escape these drugs." Researchers believe they will be able to effectively target cancer stem cells with the next generation of therapies.

Link: http://www.nlm.nih.gov/medlineplus/news/fullstory_35897.html