Table 5.

Joint effects of smoking and substantial silica exposure on risk of lung cancer, studies I and II pooled

ExposureSmoking level
0 cigarette-years>0 to <400 cigarette-years≥400 to <1,000 cigarette-years≥1,000 cigarette-years
Ca/CoOR (95% CI)*Ca/CoOR (95% CI)*Ca/CoOR (95% CI)*Ca/CoOR (95% CI)*
Unexposed24/298143/2382.19 (1.28-3.76)278/4676.91 (4.40-10.85)816/55316.90 (10.87-26.28)
Any level of exposure 7/651.28 (0.52-3.17)14/503.20 (1.51-6.77)74/1256.76 (4.01-11.40)313/16023.20 (14.41-37.36)
Nonsubstantial exposure4/500.98 (0.32-3.00)11/383.09 (1.36-7.00)51/965.98 (3.44-10.40)222/11822.00 (13.46-35.96)
Substantial exposure3/152.25 (0.59-8.56)3/123.67 (0.95-14.14)23/299.49 (4.68-19.24)91/4226.93 (15.16-47.84)
  • *Adjusted for several covariates determined a priori, including original study (i.e., study I or II), age, ethnicity, proxy respondent, education level, natural logarithm of median postal code region income, and occupational exposure to respirable asbestos, benzo(a)pyrene, chromium VI, and diesel emissions.