Immunological Parameters in Photocarcinogenesis

Abstract

Epidermal cancers, basal cell epitheliomas, and squamous cell carcinomas are by far the most common of human malignancies. The primary stimulus for the development of these tumors is irradiation from the sun. Examination of the sun’s role in the production of human skin cancers does not lend itself to direct experimentation. However, extensive astute observations have strongly suggested the etiological significance of light energy in the induction of these tumors (Urbach et al., 1974). Skin cancers in whites occur most frequently on sun-exposed parts of the body and in general are most prevalent in geographical areas of the greatest insolation and among people who receive the most exposure, i.e., men who work outdoors. They are rare in blacks and other deeply pigmented individuals who have the greatest protection against ultraviolet (UV) injury. Furthermore, the lighest-complexioned individuals, such as those of Scottish and Irish descent, appear to be most susceptible to skin cancer formation when they live in geographical areas of high UV exposure. When skin cancers do occur in the darkly pigmented races, they are not distributed primarily in the sun-exposed areas as they are in light-skinned people. The tumors in these pigmented individuals are most commonly stimulated by other forms of trauma such as chronic leg ulcers, irritation due to the lack of wearing shoes, the use of kangeri (an earthenware pot which is filled with burning charcoal and strapped to the abdomen for warmth), the wearing of a dhoti (loin cloth), and so on. In contrast, the distribution of skin cancer in the Bantu albino and in pigmented patients with xeroderma pigmentosum follows sun-exposure patterns.