MODEL RELEASED. Xeroderma pigmentosum. Skin cancer on the forehead of a patient with xeroderma pigmentosum (XP). XP is a genetic defect that causes deficiency in the skin's ultraviolet light damage repair mechanisms. Consequently sufferers are extremely sensitive to sunlight, which causes blistering, premature skin ageing, blindness, and progressive neurological disorders. Skin cancers are prevalent among patients with XP. There is no treatment. Instead, sufferers must avoid exposing their skin to sunlight wherever possible by staying indoors or using sunblock, sunglasses and protective clothing. Skin cancer may be treated by surgical excision and radiotherapy.