Skin Stem Cells in Cancer

Stem cells (SCs) are responsible for maintaining and regenerating tissues and show unique defining characteristics, including self-renewal, asymmetrical cell division, low proliferation rate, and clonogenic potential. Niches of epidermal SCs have been identified in the bulge of hair follicles, the basal layer of the interfollicular epidermis, and the base of sebaceous glands. Accumulating evidence suggests that multipotent bulge cells generate hair follicles under physiological conditions and regenerate the epidermis and sebaceous glands in response to skin injury. In contrast, SCs of the interfollicular epidermis and sebaceous glands are lineage specific and generate their respective tissues without recruiting SCs from the bulge compartment. Cancer stem cells (CSCs) represent a class of tumor cells exhibiting stem cell-like properties and ability to initiate tumors. They are derived from SCs or from non-stem cells that acquire self-renewal potential. Likely SCs, CSCs express regulatory factors of self-renewal, such as SOX2, MYC, and OCT4, and some common “stemness” pathways, such as Wnt signaling. In contrast, they could not be multipotent and lead to single lineage tumors, such as squamous cell carcinoma (SCC) (epidermal lineage), various follicular tumor types (hair follicle lineage), and sebaceous gland tumors (sebaceous lineage). Currently, several studies on CSC biology have been performed to develop new targeted therapies for patients with skin tumors with poor prognoses.