The interaction between smoking status and highly active antiretroviral therapy (HAART) use on the risk of Kaposi's sarcoma (KS) in a cohort of HIV-infected men

BACKGROUND: Although the independent effects of smoking status and HAART are reported as lower risks against KS, their combined effects have not been explored. We examined whether there is an interaction between smoking status and HAART use on the risk of KS development in an on-going US cohort of HIV-infected men. METHODS: Cox proportional hazards regression was used to analyse a total sample of 2736 participants of the Multicenter AIDS Cohort Study (MACS). RESULTS: We identified 530 incident KS cases with a total follow-up time of 26 594 person-years (incidence rate: 2.00 out of 100 person-years). Current smoking status and HAART use were independently associated with a lower risk of KS development (hazard ratio – HR=0.56, 95% CI: 0.35–0.90, P=0.02 and HR=0.27, 95% CI: 0.16–0.48, P<0.0001, respectively). There was no evidence of multiplicative interaction between current smoking status and HAART use on KS risk (HR=2.14, 95% CI: 0.97–4.73, P(interaction)=0.06). Lower effect of smoking was only present among those not on HAART (HR=0.57, 95% CI: 0.35–0.92, P=0.02). CONCLUSION: The inverse association of cigarette smoking on KS risk may be limited to those not on HAART. The biological mechanism of smoking in KS carcinogenesis should be elucidated.