Polymorphic light eruption and skin cancer prevalence: is one protective against the other?

Abstract

Ultraviolet (UV) radiation (UVR) interacts with chromophores in cutaneous cells with consequent antigenicity. The normal response to this is a downregulation of immune responsiveness. Failure of the immune system to downregulate and to ignore transient photoantigens in human skin results in polymorphic light eruption (PLE), the commonest of the photodermatoses. UVR initiates and promotes skin cancer (SC): UV-induced immunosuppression permits the expansion of UV-mutated clones of cells which ultimately lead to SC. Because there is increased immune surveillance and resistance to immune suppression following UVR exposure in PLE one might expect a protective effect of PLE against SC and, conversely, a reduced risk of PLE among patients with SC. We therefore constructed a prospective case-control study to see if this were the case. Two groups were studied: a group comprising 214 patients with SC and 210 gender- and aged-matched controls, and a group comprising 100 patients with PLE and 155 gender- and aged-matched controls. Each participant answered a questionnaire aimed at establishing personal and family history of SC and photodermatoses. Skin type and exposure to UVR were also documented. The prevalence of PLE in people with SC was 7.5%, compared with 21.4% for controls (P<0.001). The prevalence of SC in patients with PLE was 4% compared with 7.1% for controls. Our results show (i) strong evidence of reduced PLE in patients with SC, and (ii) a trend for reduced SC in patients with PLE. The immunological basis of PLE may therefore confer protection against SC.