Malignant tumours and psoriasis: climatotherapy at the Dead Sea

In this retrospective, nation-wide cohort study, the risk of cancer was assessed for 1738 Danish patients with psoriasis subjected to climatotherapy at the Dead Sea during 1972-93, by linkage to the Danish Cancer Registry. The overall risk of cancer in patients treated at the Dead Sea (standardized incidence ratio, SIR = 1.59) was higher than that expected in the general population, owing to an excess risk of non-melanoma skin cancer (NMSC) [SIR = 4.2 for basal cell carcinoma (BCC) and 10.7 for squamous cell carcinoma (SCC)]. In addition, the distribution of NMSC among body sites, age groups and sexes was unusual in those treated at the Dead Sea, favouring NMSC in young individuals and at multiple sites (SIR = 10.7 for BCC and 57.2 for SCC), multiple BCCs being particularly common among young women. Thus, people subjected to climatotherapy at the Dead Sea for psoriasis constitute a high-risk group for NMSC, SCC in particular, but not for malignant diseases in general. The study design precludes conclusions on whether climatotherapy plays a specific part in skin carcinogenesis which is different from other sources of ultraviolet (UV) radiation, as climatotherapy is inevitably confounded by excess UV exposure.