Sunlight, DNA damage and skin cancer: a new perspective

A study on the effects of seasonal solar radiation on exposed populations

In the present study the effects of seasonal solar radiation (summer and winter) on exposed populations of two different age groups (20-25 and 40-55 years old) were investigated. In addition, the effects of external factors, such as hydrogen peroxide (H(2)O(2)) and gamma-irradiation, as well as the repair efficiency of human lymphocytes from these populations, was also evaluated. Our results show that the amount of DNA damage appears to be influenced by the exposure to solar radiation, with the summer exposure being the most damaging. Age was also found to be a significant factor, with the older population being more susceptible to solar radiation than the younger one. Season does not appear to affect the sensitivity to external DNA-damaging agents, while age does. Age was also found to have an effect on the DNA repair capacity of the examined populations.

UV-induced mutations and skin cancer: how important is the link?

Studies with patients having the inherited DNA repair disorders xeroderma pigmentosum (XP), Cockayne syndrome (CS), and sun-sensitive trichothiodystrophy (TTD) have shown that neither the defect in repair nor the consequent elevated frequency of sunlight-induced mutations in the skin is sufficient to account for the classically high incidence of skin cancer in XP patients. The possible ways in which different mutations in the XP(D) gene and deficiencies in the immune system may be involved are discussed.

The risk of non-melanoma skin cancer incidence in the Japanese atomic bomb survivors

The latest Japanese atomic bomb survivor non-melanoma skin cancer incidence dataset is analysed and indicates substantial curvilinearity in the dose-response curve, consistent with a possible dose threshold of about 1 Sv, or with a dose-response in which the excess relative risk is proportional to the fourth power of dose, with a turning-over in the dose-response at high doses (> 3 Sv). The time distribution of the radiation-induced excess risk is best described by a model in which the relative excess risk is proportional to a product of powers of time since exposure and attained age. The fits of generalized relative risk models with exponential functions of time and age at exposure (and in particular of attained age) to adjust the relative risk are less satisfactory, as also are the fits of other models in which products of powers of time since exposure, age at exposure and attained age adjust the excess absolute risk. Sensitivity analyses indicate the importance of likely adjustments to the Hiroshima neutron doses for the optimal model parameters, particularly if values of the neutron relative biological effectiveness (RBE) of more than 5 are assumed. If adjustments recently proposed are made to the Hiroshima neutron doses, then using the optimal model (in which excess risk is proportional to the fourth power of dose) the best estimate of the neutron RBE is 1.3 (95% CI < 07.1). However, uncertainties in skin dose estimates for the atomic bomb survivors means that the findings with respect to the neutron RBE and the non-linearity in the dose-response curve should be treated with caution.

Sun exposure and non-melanocytic skin cancer

Non-melanocytic skin cancer has long been regarded as one of the harmful effects of solar ultraviolet (UV) radiation on human health. In this review, we examine epidemiologic evidence linking sun exposure and skin cancer coming from both descriptive studies in populations and analytical studies involving estimates of exposure in individuals. Particular attention is given to the quality of the published data. The epidemiologic evidence that sun exposure causes skin cancer is mainly indirect. Incidence or mortality is inversely related to latitude in populations of mainly European origin (e.g., the United States, Australia), and is higher in people born in Australia (high ambient solar radiation) than in migrants to Australia from the United Kingdom (lower ambient radiation). Skin cancer occurs mainly at sun-exposed body sites and in people who are sensitive to the sun; a reduced capacity to repair UV-induced DNA damage appears to increase the risk. The direct evidence linking sun exposure and skin cancer is weaker with few well-conducted studies of sun exposure in individuals. Mostly, studies of total sun exposure have not found statistically significant positive associations; those that did, had not adjusted for potential confounding by age and gender and thus their interpretation is limited. Studies of occupational sun exposure had relative risks not greater than 2.0; recreational exposure has been little studied. Other measurements, less direct but potentially less prone to measurement error, are sunburn (not evidently associated with skin cancer risk) and indicators of benign cutaneous sun-damage (strongly associated but lacking empirical evidence that sun exposure is their main cause). Many questions remain about the relationship between sun exposure and skin cancer.

Squamous cell carcinoma of the skin (excluding lip and oral mucosa)

The striking impression obtained from reviewing the cancer literature is how difficult it is to analyze the data for answers to many important biologic, behavioral, prognostic, and therapeutic questions about squamous cell carcinoma of the skin. This article addresses current concepts, controversies, and management of cutaneous squamous cell carcinoma (excluding the lip and oral mucosa).