EVIDENCE OF AN ASSOCIATION BETWEEN NON-HODGKINS-LYMPHOMA AND SKIN-CANCER

Objective-To investigate a possible Link between exposure to ultraviol et light and the almost epidemic increase in non-Hodgkin's lymphoma wo rldwide. Because ultraviolet light is known to cause skin cancers, the association between non-Hodgkin's lymphoma and skin cancer was studie d. Design-Secondary occurrence of either malignant melanoma or squamou s cell skin cancer in cohorts of patients with a first diagnosis of ei ther non-Hodgkin's lymphoma or chronic lymphocytic leukaemia, and vice versa, were studied. Expected numbers of subsequent cancers were calc ulated by sex, age, and period specific national incidence rates multi plied by the person years under observation in the cohorts. Setting-De nmark (1943-89) and Sweden (1958-89). Subjects-Four population based c ohorts identified in the nationwide cancer registries (34641 people wi th non-Hodgkin's lymphoma, 17400 with chronic lymphocytic leukaemia, 3 4989 with malignant melanoma, 25980 with squamous cell skin cancer). A total of 562085 person years were accrued for the analysis. Main outc ome measures-The ratios of observed to expected cancers (the standardi sed incidence ratio) served as a measure of the relative risk. Results -The relative risk for developing squamous cell skin cancer was 5.5 (9 5% confidence interval 4.6 to 6.6) among patients with non-Hodgkin's l ymphoma and 8.6 (7.2 to 10.3) among patients with chronic lymphocytic leukaemia. The relative risks remained high over more than IS years of follow up. Relative risks for malignant melanoma were 2.4 (1.8 to 3.2 ) for patients with non-Hodgkin's lymphoma and 3.1 (2.1 to 4.4) for pa tients with chronic lymphocytic leukaemia. After aquamous cell skin ca ncer had been diagnosed there was a twofold excess risk for non-Hodgki n's lymphoma and chronic lymphocytic leukaemia. By contrast, in each o f the cohorts the general cancer risks excluding skin and lymphoprolif erative malignancies were close to the expected. Conclusions-The occur rence of non-Hodgkin's lymphoma and skin cancer are strongly associate d; this supports the hypothesis that the secular increase in exposure to ultraviolet light may have contributed to the increasing incidence of non-Hodgkin's lymphoma in recent decades