Does intermittent sun exposure cause basal cell carcinoma? a case-control study in Western Australia

The multicentre south European study 'Helios'. II: Different sun exposure patterns in the aetiology of basal cell and squamous cell carcinomas of the skin

The role of sun exposure in development of basal cell and squamous cell carcinomas among different populations from south Europe was investigated. Between 1989 and 1993 we interviewed incident cases and a random population sample of controls from five centres where a cancer registry was operating, whereas we selected a sample of hospital-based cases and controls from the other three centres. We gathered information on life-long exposure to sunlight during different activities. Results are analysed for 1549 basal cell carcinoma (BCC) cases and 228 squamous cell carcinoma (SCC) cases compared with 1795 controls. We observed a statistically significant increase of risk of SCC with increasing sun exposure beyond a threshold of 70,000 cumulated hours of exposure in a lifetime. Sun exposures during work and holidays were, however, inversely correlated. Odds ratios (ORs) of SCC were up to eight or nine times the reference for the highest exposures (200,000 cumulated hours or more). BCC exhibited a 2-fold increase of risk for lower exposure (8000-10,000 cumulated hours in a lifetime) with a plateau and a slight decrease of risk for the highest exposures (100,000 cumulated hours or more). Outdoor work showed a significantly increased risk of SCC (OR 1.6 for more than 54,000 cumulated hours of exposure in a lifetime), whereas recreational activities such as sun exposure during holidays at the beach (OR 1.6 for more than 2600 cumulated hours of exposure in a lifetime) or during water sports (OR 1.6 for more than 2600 cumulated hours of exposure in a lifetime) were associated with an increased risk of BCC. Risk patterns were different in poor or good tanners with a significant risk trend for good tanners, whereas poor tanners were on a plateau of increased risk at any level of exposure. Solar radiation is associated with a risk of BCC even for relatively short periods of exposure such as during holidays and sports, whereas SCC develops later if exposure continues. The skin's ability to tan modulates the risk of BCC; subjects who tan poorly have a steady risk increase, whereas people who tan easily develop cancer only after prolonged exposures.

The multicentre south European study 'Helios'. I: Skin characteristics and sunburns in basal cell and squamous cell carcinomas of the skin

The aim of this study was to investigate constitutional and environmental determinants of non-melanocytic skin cancer among different populations from south Europe. Between 1989 and 1993 we interviewed incident cases and a random population sample of controls from five centres where a cancer registry was operating, whereas we selected a sample of hospital-based cases and controls from three other centres. Controls were stratified according to the age and sex distribution of cases. In all, 1549 cases of basal cell carcinoma (BCC), 228 of squamous cell carcinoma (SCC) and 1795 controls were interviewed. Both cancers affected primarily sun-exposed sites such as face, head and neck, but the prevalence of BCC on the trunk was higher than for SCC. Pigmentary traits such as hair and eye colour as well as tendency to sunburn were strong and independent indicators of risk for both BCC and SCC. In SCC, adjusted odds ratios (ORs) ranged from 1.6 for fair hair colour to 12.5 for red hair. Light-blonde hair entailed a risk of about 2 for BCC. Pale eye colour was associated with a risk of 1.8 for SCC and 1.4 for BCC. Subjects who always burn and never tan showed an adjusted OR of 2.7 for BCC and 2.0 for SCC. A history of sunburns and a young age at first sunburn were associated with an increased risk for BCC only (OR 1.7). Pigmentary traits and sun sensitivity of the skin confirmed their role as risk indicators. The effect of sunburns, as an indicator of both exposure and sun sensitivity of the skin, is less clear. Nevertheless, its association with BCC suggests, by analogy with melanoma, a relationship with intense sun exposure. Conversely, SCC would require prolonged exposure to sunlight.

Sun exposure and skin disease

Sunlight exposure produces a variety of adverse cutaneous effects. Erythema, photosensitivity, and immunologic alterations represent acute events, whereas photoaging and carcinogenesis are long-term consequences. These adverse cutaneous sequelae can be minimized by photoprotection in the form of sun avoidance, regular cover-up with clothing, and sunscreen application. This chapter reviews the diagnosis and treatment of sun-related skin disorders and recommendations for reducing photodamage.

A dose-response curve for sun exposure and basal cell carcinoma

A population-based case-control study of sun exposure and basal cell carcinoma (BCC) was conducted in Western Australia in 1988. Its aim was to examine the relationship between risk of BCC and the amount and pattern of sun exposure. This report deals with amount of exposure. The odds ratios (ORs) for BCC on the head and neck and limbs decreased with increasing total exposure, whereas the opposite was observed for BCC on the less heavily exposed trunk, with the highest OR in those with the greatest exposure. In an analysis of all body sites together in which the total hours of exposure to the specific site was treated as a continuous variable, an initial rise in risk of BCC was seen with a peak OR of 1.4 at about 35,000 hr of exposure, followed by a fall. In contrast to these site-specific patterns, lifetime accumulated sun exposure of the whole body showed no appreciable association with BCC either in total or for working days only. Risk of BCC was positively associated with lifetime exposure on non-working days, however, with an OR for higher than baseline categories of around 1.7. There was a significant interaction between ability to tan and total and occupational sun exposure. Risk increased with increasing exposure in those who tanned well but not in those who tanned poorly. This pattern is consistent with other observations which indicate that beyond a certain level of sun exposure risk of BCC does not increase further.