Skin cancer

Many epidemiological studies have implicated solar radiation as a cause of skin cancer (both melanotic and non-melanotic) in fair-skinned humans (146,147). Non-melanotic skin cancers are of two major histological types: basal cell carcinoma and squamous cell carcinoma. The risk of these cancers has generally been thought to correlate with cumulative lifetime exposure to solar radiation. Nevertheless, recent evidence suggests that the relationship is more complex. At least for basal cell carcinoma, childhood exposure may be important (148-150). These types of cancer usually develop on the

Table 5. The main effects of solar ultraviolet radiation on the health of humans

Nature of effect

Direction of effect

Strength of evidence

Effect on immunity and infection Suppression of cell-mediated immunity Increased susceptibility to infection Impairment of prophylactic immunization Activation of latent virus infections

Harmful (?) Harmful Harmful Harmful

Sufficient Sufficient Inadequate Sufficient

Effects on the eye

Acute photokeratitis and photoconjunctivitis Harmful Sufficient

Climatic droplet keratopathy Harmful Limited

Pterygium Harmful Limited

Cancer of the conjunctiva Harmful Inadequate

Lens opacity (cataract) Harmful Limited

Uveal melanoma Harmful Limited

Acute solar retinopathy Harmful Sufficient (?)

Macular degeneration Harmful Inadequate

Effects on the skin Malignant melanoma Non-melanocytic skin cancer Sunburn

Chronic sun damage Photodermatoses

Harmful Harmful Harmful Harmful Harmful

Sufficient

Sufficient

Sufficient

Variable

Sufficient

Other direct effects

Vitamin D production Beneficial

Other types of cancer Beneficial

General wellbeing Beneficial

Indirect effects

Effects on climate, food supply, disease vectors, Probably air pollution, etc. harmful

Sufficient

Inadequate

Inadequate

Inadequate

Source: Armstrong (144).

parts of the body most often exposed to sunlight (such as the face, neck, scalp, hands and arms) (151,152).

Malignant melanoma, a cancer of the pigment-producing cells of the skin, usually develops on an already pigmented patch such as a mole (153-155). The relationship between melanoma skin cancer and ultraviolet radiation is complex. Overall, 60-90% of melanoma cases in fair-skinned populations are estimated to involve sunlight exposure (156). Repeated severe sunburn episodes in early life are considered important for the development of melanoma. The incidence of melanoma in fair-skinned populations has risen by 3-7% every year since at least the 1960s, which probably reflects a progressive increase in the average levels of personal exposure to solar radiation, owing to changes in the patterns of settlement, recreation, clothing and occupation that are unrelated to stratospheric ozone depletion (157).

Estimates have been made of how ozone depletion may affect the rate of skin cancer in certain countries. The model developed by Slaper et al. (158) takes into account the production and emission of ozone-depleting substances, the global stratospheric concentrations of chlorine, the local depletion of stratospheric ozone, the resulting increases in ultraviolet B levels and, finally, the effects on skin cancer rates. Several delay mechanisms in the effect of ozone depletion on skin cancer rates are important, such as the time taken to develop tumours. In the case of ozone depletion, the separate scenarios modelled are related to the Montreal Protocol, the international agreement restricting the production of ozone-depleting substances. Thus, full compliance with the Montreal Protocol and all its amendments and adjustments would lead to a peak in stratospheric chlorine concentration and ozone depletion by about 2000 (Fig. 6) and to a peak in skin cancer by about 2050. The latter is mainly delayed because skin cancer incidence depends on the cumulative ultraviolet B exposure.

The most recent assessment by the United Nations Environment Programme (54) has updated the above projections for total skin cancer for a "European" population living at a latitude around 45 °N. It estimates that, under the amended Montreal Protocol, an excess incidence will peak at about 5% during the third quarter of the 21st century. This means an extra 100 cases of skin cancer per million population per year from stratospheric ozone depletion. The current background rate of skin cancer is about 2000 cases of skin cancer per million population per year. If the moderate aging of the "European" population were factored into the modelling, the excess incidence would become, proportionally, a little higher. The calculations by the United Nations Environment Programme assume that behavioural and demographic risk factors do not change and that the current rate of ozone depletion and increases in exposure to ultraviolet radiation are sustained during the next several decades.

Was this article helpful?

0 0
How To Prevent Skin Cancer

How To Prevent Skin Cancer

Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.

Get My Free Ebook


Post a comment