Xeroderma pigmentosum (XP), is a rare, autosomal recessive disease with sun sensitivity and multiple neoplasms in association with reduced DNA repair. As a reflection of the clinical consequences of deficient DNA repair, XP serves as a model for determining the effects of proficient DNA repair. To estimate the risk of developing neoplasms in XP, we abstracted reports of 726 XP patients (from 41 countries) published from 1874 to 1982. Despite limitations of a literature survey, the XP patients under age 20 years had an estimated 2000-fold increase in frequency of basal cell and squamous cell carcinoma of the skin, of cutaneous melanoma, of cancer of the anterior eye, and of cancer of the anterior tongue, in comparison to the general population. These sites are all potentially exposed to u.v. radiation, a strong carcinogen which produces DNA damage that is poorly repaired by XP cells. XP patients under age 20 years also had an estimated 12-fold increase in occurrence of neoplasms in sites not exposed to u.v. radiation. Among the XP patients under age 40 years with internal cancer, there was a disproportionate representation of malignant neoplasms of the brain (especially sarcomas), and oral cavity (excluding tongue) compared to US whites under age 40 years. These internal neoplasms may be related to exposure to chemical environmental carcinogens that cause DNA damage which, like u.v.-induced damage, is poorly repaired by XP cells. These reports provide no evidence of an increase in XP of common lethal neoplasms such as lymphomas, or female genital tract or endocrine system cancers. These findings suggest that DNA repair plays a role in protection against u.v.-induced neoplasia and in protection against some internal neoplasms in the general population.

Recent reports of stratospheric ozone depletion have prompted concerns about the levels of solar ultraviolet radiation that reach the earth's surface. Since 1974 a network of ground-level monitoring stations in the United States has tracked measurements of biologically effective ultraviolet radiation (UVB, 290 to 330 nanometers). The fact that no increases of UVB have been detected at ground levels from 1974 to 1985 suggests that meteorological, climatic, and environmental factors in the troposphere may play a greater role in attenuating UVB radiation than was previously suspected.

The Third National Cancer Survey, 1969-71, reported 432 patients with noncutaneous melanoma, 79% originating in the eye. As with skin melanoma, ocular tumors were more common in whites than blacks and predominated in females at younger ages and males after middle life. On the other hand, ocular melanoma did not show the strong North-South gradient seen with skin melanoma; this suggested no relation to sunlight exposure.

That sunlight leads to skin cancer has been generally accepted for nearly a century. Physical data are, for the first time, available which support this hypothesis. The authors have found that a simple power relationship can be used to describe the data and that the form of this power function suggests that the risk of nonmelanoma skin cancer is related to cumulative lifetime ultraviolet (UV) exposure and that the risk of melanoma skin cancer is related to annual UV exposure. The authors emphasize that skin cancer risk also depends on location-specific demographic variables other than ultraviolet radiation.

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