The epidemiology of UV induced skin cancer

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Abstract

There is persuasive evidence that each of the three main types of skin cancer, basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and melanoma, is caused by sun exposure. The incidence rate of each is higher in fairer skinned, sun-sensitive rather than darker skinned, less sun-sensitive people; risk increases with increasing ambient solar radiation; the highest densities are on the most sun exposed parts of the body and the lowest on the least exposed; and they are associated in individuals with total (mainly SCC), occupational (mainly SCC) and non-occupational or recreational sun exposure (mainly melanoma and BCC) and a history of sunburn and presence of benign sun damage in the skin. That UV radiation specifically causes these skin cancers depends on indirect inferences from the action spectrum of solar radiation for skin cancer from studies in animals and the action spectrum for dipyrimidine dimers and evidence that presumed causative mutations for skin cancer arise most commonly at dipyrimidine sites. Sun protection is essential if skin cancer incidence is to be reduced. The epidemiological data suggest that in implementing sun protection an increase in intermittency of exposure should be avoided, that sun protection will have the greatest impact if achieved as early as possible in life and that it will probably have an impact later in life, especially in those who had high childhood exposure to solar radiation.

Introduction

By skin cancer we mean the three commonest types, basal cell (BCC) and squamous cell (SCC) carcinomas of the skin (also referred to, collectively, as nonmelanocytic skin cancer) and cutaneous malignant melanoma (melanoma).

That UV radiation per se causes these cancers is mainly an indirect inference from evidence that exposure to solar radiation, the main source of exposure to UV radiation, is their main cause and the fact that only UV radiation can damage DNA directly. That solar radiation causes these skin cancers is based on a substantial body of indirect and direct epidemiological studies. These studies are strongly supported by experimental evidence of the capacity of UV radiation to cause SCC and melanoma in animal models. There are no such models for BCC, although the presence of UV “signature mutations” in the TP53 gene in a high proportion of BCCs [1] provides biological evidence to support the epidemiological observations.

This paper summarises, the epidemiological evidence, as it now stands, that sun exposure causes skin cancer and then briefly describes the basis on which a causal role for UV radiation can be inferred from a combination of experimental and epidemiological data. Finally, it describes the key implications of these data for prevention of skin cancer by control of sun exposure.

Section snippets

Incidence by latitude or estimated ambient solar UV

The relationships between incidence rates of BCC and SCC in 1977–1978 and ambient solar UV across a latitude gradient are illustrated in Fig. 1 based on the data of Scotto et al. [2]. Rates increased with increasing estimated ambient solar UV (from Robertson-Berger meter observations of erythemal UV expressed as annual number of meter counts by 10−4) in ten US metropolitan populations from 47.5° N (Seattle) to 30.0° N (New Orleans). The values of R2 for the exponential relationships plotted in

Evidence that UV radiation per se causes skin cancer in humans

There is no practical way that the action spectrum for skin cancer can be measured directly in humans. Inferences, however, can be made about it in a number of ways.

First, the action spectrum for SCC has been rigorously determined experimentally in albino hairless mice [28]. This action spectrum shows an initial peak at 293 nm in the UVB range, falls to a trough at 354 nm of between 10−4 and 10−5 of the effect at the peak, rises to another small peak at 380 nm in the UVA range (still nearly 10−4

Comment

In 1992, an expert working group of the International Agency for Research on Cancer reviewed all the evidence for carcinogenicity of solar and ultraviolet radiation [33]. It concluded that: “There is sufficient evidence in humans for the carcinogenicity of solar radiation. Solar radiation causes cutaneous malignant melanoma and nonmelanocytic skin cancer”. All the epidemiological evidence that has accumulated since 1992 has strengthened this qualitative conclusion.

While we, like the

Acknowledgements

We thank Chris Goumas for doing the summary analysis of results of studies of sun exposure and nonmelanocytic skin cancer.

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