title: Susceptibility to oral cancer by genetic polymorphisms at CYP1A1, GSTM1 and GSTT1 loci among Indians: tobacco exposure as a risk modulator.
abstract: Oral cancer is the leading cancer type among Southeast Asian men and is causally associated with the use of tobacco. Genetic polymorphisms in xenobiotic-metabolizing enzymes modify the effect of environmental exposures, thereby playing a significant role in gene-environment interactions and hence contribute to the high degree of variance in individual susceptibility to cancer risk. This study investigates the role of polymorphisms at CYP1A1, GSTM1 and GSTT1 to oral squamous cell carcinoma (OSCC) in a case-control study involving 155 patients with precancerous lesions, 458 cancer patients and 729 age and habit-matched controls. Genotypes at these loci were determined by polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism performed on genomic DNA extracted from peripheral blood lymphocytes. Risk to oral cancer was estimated among different tobacco exposure groups and doses using logistic regression analysis. GSTM1 null genotype conferred 1.29-fold increased risk [95% confidence interval (CI), 1.04-1.65] to OSCC. GSTT1 null genotype, however, conferred 0.57 times reduced risk to OSCC (95% CI, 0.39-0.83), specifically among tobacco chewers (odds ratio 0.27; 95% CI, 0.14-0.53). This risk was further reduced to 0.13 times (95% CI, 0.04-0.46) with increase in lifetime exposure to tobacco. We also investigated risk conferred by these genotypes at two different intra-oral sites, buccal mucosa and tongue. We found increased susceptibility to buccal mucosa cancer among individuals carrying these genetic markers. These results support the finding that GSTM1 null genotype is a risk factor to OSCC among Indian tobacco habits; GSTT1 null genotype, however, emerged as a protective factor.
authors.affiliation: Cancer Research Institute, Advanced Center for Treatment, Research and Education in Cancer, Tata Memorial Center, Kharghar, Navi Mumbai 410 208, India.
authors.forename: Devasena
authors.initials: D
authors.lastname: Anantharaman
authors.forename: Pranay M
authors.initials: PM
authors.lastname: Chaubal
authors.forename: Sadhana
authors.initials: S
authors.lastname: Kannan
authors.forename: Rajani A
authors.initials: RA
authors.lastname: Bhisey
authors.forename: Manoj B
authors.initials: MB
authors.lastname: Mahimkar
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000453:epidemiology / Q000235:genetics*; D016022:Case-Control Studies; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005982:Glutathione Transferase / Q000235:genetics*; D006801:Humans; D015994:Incidence; D007194:India / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009062:Mouth Neoplasms / Q000453:epidemiology / Q000235:genetics*; D011110:Polymorphism, Genetic; D014029:Tobacco Use Disorder / Q000150:complications
chemical_list: D019363:Cytochrome P-450 CYP1A1; D005982:Glutathione Transferase; C413545:glutathione S-transferase T1