This study was conducted to investigate the modifying effect of
glutathione S-transferase (GST) M1 and T1 polymorphisms on
aflatoxin-induced hepatocarcinogenesis among
chronic hepatitis B virus
surface antigen (
HBsAg) carriers. A total of 79
HBsAg-positive cases of
hepatocellular carcinoma (HCC) diagnosed between 1991 and 1997 were identified and individually matched to one or two
HBsAg-positive controls on age, gender, residence and date of recruitment from the same
cancer screening cohort in Taiwan. Blood samples were tested for
hepatitis B and C
viral markers by
enzyme immunoassay and for
aflatoxin B(1) (AFB(1))-albumin adducts by competitive
enzyme-linked
immunosorbent assay. GSTM1 and GSTT1 genotypes were determined by PCR. There was a statistically significant relationship between detectable levels of AFB(1)-albumin adducts in serum and risk of HCC among chronic
HBsAg carriers, with an adjusted odds ratio (OR) of 2.0 [95% confidence interval (CI) 1.1-3.7]. In addition, the effect of
aflatoxin exposure on HCC risk was more pronounced among chronic
HBsAg carriers with the GSTT1 null genotype (OR 3.7, 95% CI 1.5-9.3) than those who were non-null (OR 0.9, 95% CI 0.3-2.4). The interaction between serum AFB(1)-albumin adduct level and GSTT1 genotype was statistically significant (P = 0.03). For GSTM1 the effect of
aflatoxin exposure on HCC risk in those with the null genotype was also greater (adjusted OR 2.8, 95% CI 1.0-7.8) than in those with the gene present (adjusted OR 1.8, 95% CI 0.8-4.5), but the difference was not significant (P = 0.91). Notably, when the interaction between
aflatoxin exposure and GSTT1 genotype was considered,
aflatoxin exposure by itself was not a significant determinant of HCC risk among chronic
HBsAg carriers. These results demonstrate the importance of gene-environment interactions in the multifactorial development of HCC.