Finding the root of the problem: the quest to identify melanoma stem cells

Melanoma is an exceptionally aggressive cancer with limited treatment options. As such, the idea that a minority of tumor cells, termed melanoma stem cells, are actually responsible for the progression of the disease offers up new possibilities for targeted therapies. However, reliable identification of these melanoma stem cells is complicated by the lack of clearly defined markers to distinguish them from the general tumor cell population. Additionally, there is evidence that under permissive conditions, a high proportion of melanoma cells are capable of forming tumors in mice. This review summarizes a number of the possible markers being considered for identifying melanoma stem cells, the potential role of transcription factors that regulate pluripotency and stem cell maintenance in melanoma, and evidence that may undermine the applicability of the cancer stem cell hypothesis to melanoma.