American journal of epidemiology
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In a search for clues to the origin of squamous cell skin cancer (SCC), the authors investigated the pattern of new cancers in a cohort of 5,100 SCC patients whose tumors were diagnosed during the years 1978-1989 and recorded in the Danish Cancer Registry. Subsequent cancer experiences in SCC patients were compared with the cancer incidence in the Danish population using ratios of observed cancers to expected cancers as a measure of the relative risk. Overall, patients with SCC were at increased risk of new malignancies (relative risk (RR) = 1.6, 95% confidence interval (CI) 1.5-1.7). ⋯ A previously undocumented significant excess of smoking-related cancers was observed after an SCC diagnosis, suggesting that smoking may be involved in the development of SCC. Since a variety of other squamous cell cancers have already been linked to smoking, the authors speculate that some general effect of smoking might act on all human squamous epithelia. The observed significant associations with lymphoma and leukemia and the high risk of subsequent malignancies in young SCC patients merit further attention.