Site distribution of different types of skin cancer: new aetiological clues.

Since the investigation, at an individual level, of lifetime sun exposure remains difficult the site distribution of different types of skin cancer can be an important source of aetiological clues. The present report deals with 1,149 cases of cutaneous malignant melanoma (CMM), 7,685 of basal-cell carcinoma (BCC) and 3,049 of squamous-cell carcinoma (SCC) reported between 1976 and 1992 to the Vaud Cancer Registry, in Switzerland. Site- and type-specific age-standardized (on the world population) incidence rates per 100,000 population and per 100,000 unit surface were computed, together with relative age-standardized incidence rates (i.e., rates per 100,000 surface unit in each anatomical site relative to rates for the body as a whole). The highest rates per unit surface were seen for both genders in the face, thus indicating same role of cumulative sun exposure in all skin-cancer types. Relative to the incidence in the whole body, the excess on the face was, however, more than 20-fold for BCC and SCC, but only 4-fold for CMM. The relative incidence in males was very much higher for SCC than for CMM and BCC in the neck, ears and scalp, a heavily sun-exposed area in men but not in women. Conversely, a substantial lack of SCC was seen in the trunk. In conclusion, site distribution of different skin-cancer types suggests that short-duration UV-light exposure is sufficient to increase CMM risk substantially, but has little influence on SCC risk. With the increase of exposure, however, SCC rises more steeply than BCC. Age-related behaviour (i.e., another indirect indicator of duration of exposure to UV light) is consistent with the anatomical distribution of skin cancer.