Incident testicular cancer in relation to using marijuana and smoking tobacco: A systematic review and meta-analysis of epidemiologic studies.

BACKGROUND: Recent epidemiologic studies identified credible associations between marijuana smoking and risk of nonseminomatous testicular germ cell tumors (TGCTs), but did not distinguish exposure to cannabinoid compounds from exposure to other constituents of smoke. METHODS: We implemented a systematic review of scholarly literature followed by random effects meta-analysis to quantitatively synthesize published data relating incident TGCT to each of 2 exposure histories: ever using marijuana, and ever smoking tobacco. RESULTS: We identified four epidemiologic studies of marijuana use and 12 of tobacco smoking. Summary data concur with earlier reports of a specific association of marijuana use with nonseminoma, summary odds ratio [sOR] = 1.71 (95% confidence interval [CI] 1.12-2.60), and identify a positive association, sOR = 1.18 (95% CI 1.05-1.33), between tobacco smoking and all TGCT. CONCLUSIONS: Available data accord with positive associations between incident TGCT and each exposure, implicating both cannabinoid compounds and other constituents of smoke. Etiologic interpretation awaits epidemiologic studies that assess associations between tobacco smoking and nonseminomatous TGCT, investigating not only these exposures but also both co-use of tobacco and marijuana and smoke-free sources of cannabinoids, while adequately evaluating potential confounding among all of these exposures.