Risk of classic Kaposi sarcoma with exposures to plants and soils in Sicily

BACKGROUND: Ecologic and in vitro studies suggest that exposures to plants or soil may influence risk of Kaposi sarcoma (KS). METHODS: In a population-based study of Sicily, we analyzed data on contact with 20 plants and residential exposure to 17 soils reported by 122 classic KS cases and 840 sex- and age-matched controls. With 88 KS-associated herpesvirus (KSHV) seropositive controls as the referent group, novel correlates of KS risk were sought, along with factors distinguishing seronegatives, in multinomial logistic regression models that included matching variables and known KS cofactors - smoking, cortisone use, and diabetes history. All plants were summed for cumulative exposure. Factor and cluster analyses were used to obtain scores and groups, respectively. Individual plants and soils in three levels of exposure with P(trend )≤ 0.15 were retained in a backward elimination regression model. RESULTS: Adjusted for known cofactors, KS was not related to cumulative exposures to 20 plants [per quartile adjusted odds ratio (OR(adj)) 0.96, 95% confidence interval (CI) 0.73 - 1.25, P(trend )= 0.87], nor was it related to any factor scores or cluster of plants (P = 0.11 to 0.81). In the elimination regression model, KS risk was associated with five plants (P(trend )= 0.02 to 0.10) and with residential exposure to six soils (P(trend )= 0.01 to 0.13), including three soils (eutric regosol, chromic/pellic vertisol) used to cultivate durum wheat. None of the KS-associated plants and only one soil was also associated with KSHV serostatus. Diabetes was associated with KSHV seronegativity (OR(adj )4.69, 95% CI 1.97 - 11.17), but the plant and soil associations had little effect on previous findings that KS risk was elevated for diabetics (OR(adj )7.47, 95% CI 3.04 - 18.35) and lower for current and former smokers (OR(adj )0.26 and 0.47, respectively, P(trend )= 0.05). CONCLUSIONS: KS risk was associated with exposure to a few plants and soils, but these may merely be due to chance. Study of the effects of durum wheat, which was previously associated with cKS, may be warranted.