Skin cancer in humans is sometimes associated with an injury. In this image depicting the underside of a mouse's skin, tiny tumors appearing as finger-like projections (center) extend outwards from a wound site that has previously healed. These tumors were seeded by stem cells originating from hair follicles at the periphery of the wound. These hair follicles appear as large stalks at the edges of this photo. During the normal repair process, hair follicle stem cells are mobilized into the site of injury to regenerate lost skin. If these stem cells turn on oncogenic genes, tumors can result.