Stem-cell hierarchy in skin cancer.

Tumour architecture mimics many of the features of normal tissues, with a cellular hierarchy that regulates the balance between cell renewal and cell death. Although many tumours contain cells with the characteristics of stem cells, the identity of the normal cells that acquire the first genetic hits leading to initiation of carcinogenesis has remained elusive. Identification of the primary cell of origin of cancers and the mechanisms that influence cell-fate decisions will be crucial for the development of novel non-toxic therapies that influence tumour-cell behaviour.