Genetic and environmental interactions on oral cancer in southern Thailand

Many countries are interested in understanding the relationship between gen etic susceptibility and their prevalent environmental cancers for disease p revention. In Thailand we conducted a population-based case-control study o f 53 matched pairs to assess the risk of oral cancer in relation to genetic polymorphism of the glutathione-S-transferase genes (GSTM1 and GSTT1) in c igarette smokers, alcohol drinkers, and betel quid chewers. Interaction of the genes with other potential risk factors such as local bean consumption were also elucidated. Homozygous deletion of GSTM1 has a frequency of 56.6% (n = 30 over 53) among the patients and 30.2% (16/53) among the controls. This gene is associated with a 2.6-fold higher risk for development of oral cancer (95% Cl 1.04-6.5). Among the null GSTM1 individuals, those who smok e, consume alcohol, and/or chew betel quid have a significantly increased r isk for oral cancer with an odd ratio (OR) = 4.0 (95% CI = 1.2-13.7), OR = 7.2 (95% CI = 1.5-33.8), and OR = 4.4 (95% CI = 1.1-17.8), respectively. In teractions between any two of the lifestyle habits for oral cancer risk, ho wever, are not found. The frequency of the GSTT1 null genotype is 34.0% (18 /53) among the patients and 47.2% (25/53) among our controls. There is no a ssociation between the GSTT1 null allele and oral cancer risk. In conclusio n, our study provides data to indicate that individuals who have homozygous deletion of the GSTM1 gene have increased risk for oral cancer. The risk i ncreases further when these individuals are exposed to environmental toxica nts such as chemicals in cigarette smoke, alcohol, and betel quid. These ba seline data can be applied to a larger population-based study, both to veri fy the observation and to conduct mechanistic investigations. (C) 2001 Wile y-Liss, Inc.