Objective: To examine the incidence of first diagnosis of invasive squamous cell carcinoma (SCC) of the skin over time. Design: Retrospective, population-based incidence study. Setting: Enumerated, geographically isolated, semiurban population served by the Mayo Clinic and its affiliated hospitals and the Olmsted Medical Center, including its affiliated hospital in Rochester, Minn. Methods: Using the Rochester Epidemiology Project databases that capture virtually all medical care provided to the residents of Rochester, we identified and reviewed records of all documented residents in whom histologically proven, invasive SCC of the skin was first diagnosed between 1984 and 1992. Age and sex stratum-specific rates were calculated, and age-adjusted rates observed over time for individuals aged 35 years or older were analyzed using Poisson regression. Adjusted rates were compared with the results of other studies. Results: Review of 1630 records identified 511 incidence cases of SCC. Tumors located on the head and neck accounted for 66.4% of tumors in females and 72.9% in males. The annual age- and sex- specific incidence rates per 100 000 increased from 0 cases among males aged 0 to 14 years to 1286.0 cases among males aged 85 years or older. Over time, the annual age-adjusted incidence rates per 100 000 females rose from 46.5 (95% confidence interval [CI], 32.4-60.6) for the 1984 to 1986 period to 99.6 (95% CI, 80.4-118.7) for the 1990 to 1992 period and were 71.2 (95% CI, 61.7- 80.8) overall. The corresponding rates for males were 125.9 (95% CI, 95.3156.4), 191.0 (95% CI, 156.9-225.0), and 155.5 (95% CI, 137.0-174.0). The age- and sex-adjusted SCC incidence rates for the period from 1987 to 1989 and 1990 to 1992 exceeded those for the period from 1984 to 1986 (P =.03 and P<.001, respectively). Our age-adjusted rates for SCC were within the ranges seen in other white populations from temperate climates. Conclusion: The frequencies of first diagnosis of SCC are increasing at rates beyond those explainable by demographic shifts alone.
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