Epidemiology of Kaposi's sarcoma in Sweden prior to the acquired immunodeficiency syndrome.

We studied retrospectively 529 cases of Kaposi's sarcoma (KS) reported to the Swedish Cancer Registry between 1958 and 1982 to determine incidence rates, survival and rate ratios, together with the frequency and types of associated malignancies. The age-standardized (Swedish population 1970) incidence rate generally increased over the time period, with a mean of 0.27 cases per 100,000 population per year (males 0.40, females 0.14). The incidence rate ratio (based on 5-year intervals and relative to the earliest period) reached 2.06 for males and 3.76 for females in the 1968-1972 interval, while the actual peak occurred between 1971 and 1974 for both sexes. Poisson regression modelling suggested a transient shift in the age-specific male incidence rate pattern with a relative increase of the disease in younger age groups (p = 0.05) up to 1968-1972. The age-adjusted male:female ratio did not change significantly from 2.9 during the period of study. In relation to the general population, 18% fewer men and 24% fewer women were alive 10 years after the diagnosis had been made. Ninety-nine (19%) cases had other primaries, of which 17 were neoplasms of lymphocytic origin. Lymphoproliferative malignancy was 2.5 times (95% CI 1.38, 4.37) more common than expected in patients with KS (in particular in females) but a definite increase in other malignancies was not apparent. It is questionable whether immune dysfunction due to other malignant disease or drug therapy can account for the epidemiologic changes in KS, which began almost 2 decades prior to the AIDS epidemic in Sweden.