Dietary Isothiocyanates, Glutathione S-Transferase M1 (GSTM1), and Lung Cancer Risk in African Americans and Caucasians from Los Angeles County, California

Abstract

Isothiocyanates, found in cruciferous vegetables, are anticarcinogenic. Racial differences in smoking do not fully account for the African-American excess lung cancer incidence. African Americans consume more cruciferous vegetables than U.S. Whites. Impact on lung cancer risk is unknown. The glutathione S transferase M1 (GSTM1) gene promotes urinary isothiocyanate excretion. We evaluated dietary isothiocyanates and lung cancer using a population-based case-control study of 933 African Americans and Caucasians (non-Hispanic U.S. White) from Los Angeles County, California (311 cases; 622 controls). Broccoli, cauliflower, greens, and cabbage food-frequency variables represented isothiocyanates. Isothiocyanates were protective for lung cancer risk. Adjusted odds ratio (OR) for the uppermost quartile > 80 μ mol isothiocyanates/wk, compared to lowest, was 0.65 [95% confidence interval (CI) = 0.41–1.00, trend P = 0.02]. Association was stronger among subjects with homozygous deletion of GSTM1 (OR = 0.52, 95% CI = 0.31–0.86) than subjects with at least one GSTM1 copy (OR = 0.77, 95% CI = 0.49–1.21). The difference was not statistically significant (P = 0.16). Despite African Americans consuming more cruciferous vegetables, the isothiocyanate association did not vary by race (P = 0.52). Reduced lung cancer risk with higher isothiocyanate intake may be slightly stronger among subjects with deletion of GSTM1.