Biological Amplification Factor for Sunlight-induced Nonmelanoma Skin Cancer at High Latitudes

Abstract

Data for the incidence of basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of the skin, registered for six regions of Norway during 10 years (1976–1985), were used to evaluate the biological amplification factor A_b for induction of these cancers by sunlight. A_b is the ratio of the increment in skin cancer production to the increment in causative sunlight exposure. Two different approximations were used for the action spectrum for carcinogenesis: an erythema action spectrum; and an action spectrum for mutagenesis of cells in the basal layer of the skin. These two fundamentally different approaches yielded A_b values that were similar to within about 10%: 2.1–2.3 for BCCs; and 1.6–1.8 for SCCs. Using a radiation amplification factor for ozone depletion of 0.8–1.1, we find that the total amplification factor for BCCs is within the range 1.6–2.1 and that that for SCCs is within the range 1.3–1.7 at northern latitudes of 60–70 degrees. Thus, an ozone depletion of 1% will result in an increase in the incidence of BCCs by 1.6–2.1% and of SCCs by 1.3–1.7%. There were no significant differences between the values for men and women. Neither was there any significant difference between A_b values found for skin commonly exposed to sunlight (face) and for skin sites normally covered by clothes and therefore receiving much lower exposures, in spite of the fact that the tumor density per unit skin area was a factor of 20 or more larger at the former sites. This observation, as well as the curves relating cancer incidence with annual exposure to carcinogenic sunlight, supports a power law relationship between cancer incidence and annual sun exposure.

Sunlight appears to be the main cause of BCCs and SCCs even at the high latitudes of Northern Norway. All over, BCCs were found to be about 6 times more frequent than SCCs. The ratio of the incidence of BCCs to that of SCCs seemed to be independent of the latitude. Finally, BCCs were found to be equally frequent among men and women, while SCCs were found to be about twice as frequent among men as among women.