RISK OF 2ND CANCERS IN CLASSICAL KAPOSIS-SARCOMA

An association between Kaposi's sarcoma (KS) and malignant lymphoma ha s been suspected for many years. Both cancers belong to the group of m alignancies associated with immune suppression and have been known to occur in the same individual. Accordingly, a common etiology has been suspected. Through linkage within the Nordic cancer registries, we stu died the occurrence of cancers in a population-based cohort of 741 pat ients with classical KS. The relative risk of subsequent malignancies was expressed as the ratio of the observed numbers of cancer to the nu mbers expected based on age-, sex-, period- and country-specific incid ence rates, i.e., the standardized incidence ratio (SIR). A total of 1 04 cancers was observed during 5,802 person-years of follow-up, which was close to the expected 98.8 cases (SIR, 1.05). During the first yea r of follow-up, 3 lymphomas were observed, which is in significant exc ess of the 0.2 lymphomas expected (SIR, 13.0). In contrast, no lymphom as occurred in the period beyond the first year of follow-up vs. 2.3 e xpected. Cancers of the buccal cavity and pharynx (SIR, 10.6; n = 4) a nd of the colon (SIR, 2.7; n = 7) occurred in excess among women but n ot among men. Accordingly, our results indicate that patients with cla ssical KS are not at increased risk of cancer in general. In particula r, the overall risk of lymphomas was not significantly increased. The high relative risk of malignant lymphoma immediately after KS was base d on a limited number of cases, and this observation is unlikely to in dicate a common etiology. (C) 1997 Wiley-Liss, Inc.