GSTM1 gene polymorphism as a possible marker for susceptibility to head and neck cancers among Japanese smokers

Gene polymorphisms and risk of head and neck squamous cell carcinoma: a systematic review

Background

Exposure to the same environmental factors in different people have resulted in different susceptibility to head and neck squamous cell carcinoma (HNSCC), which suggests genetic variation may be a risk factor for the development of HNSCC. So, the aim was to review literatures on the association between gene polymorphisms and risk of HNSCCs.

Materials and methods

This systematic review included all articles on the impact of gene polymorphisms on risk and susceptibility to HNSCC published till September 2021 using PubMed, Web of science, SCOPUS, Google Scholar and Cochrane library databases.

Results

Of 1163 initial searched articles, 77 articles were eligible to include in this review. Studies were categorized based on gene functions. In each category, studied gene polymorphisms related to growth control genes, cell cycle control, apoptosis, DNA repair genes, carcinogen-metabolizing enzymes, alcohol-metabolizing genes, antioxidant gene, inflammatory cytokine, transcription factor, tumor immunity, folate metabolism, and tumor suppressor gene were discussed separately. Among the polymorphisms that are often significantly associated with HNSCC risk are: GSTM1 null, GSTT1 null, CYP2D6 *4, XRCC1 Arg194Trp and Arg399Gln, ERCC1 C8092A, XPD Lys751Gln, XRCC3 Thr241Met, P53 codon 72 and MTHFR C677T polymorphisms.

Conclusion

Varied and contradictory results have been reported in different studies regarding the association of gene polymorphisms with HNSCC risk. To conclude about this association and to overcome these contradictions, it is necessary to use the results of existing meta-analyses or to perform new or updated meta-analyses.

Effect of Polymorphisms in XRCC1, CCND1 and GSTM1 and Tobacco Exposure as Risk Modifier for Oral Leukoplakia

Analysis of gene-environment interactions may help to define the risk of oral leukoplakia. We hypothesized that an individual's susceptibility to leukoplakia is dependent on interactions between polymorphic genotypes at susceptible loci and tobacco exposure. To test this hypothesis, the relationship between tobacco use and polymorphisms in 3 genes that might contribute to variance in individuals′ susceptibility to the risk of leukoplakia was determined. In this case-control study, polymorphic genotypes in XRCC1 (399Gln), a DNA repair gene involved in removing DNA adducts, CCND1 (G870A), a key component of cell cycle regulation, and GSTM1 (null genotype), a xenobiotic-metabolizing enzyme involved in the metabolism of tobacco carcinogens, were analyzed in 100 oral leukoplakia patients and age- and gender-matched controls by PCR using genomic DNA isolated from blood. The GSTM1 null genotype was associated with a 1.6-fold increased risk of developing leukoplakia. The risk conferred by the CCND1 GA+AA variant was 2.4-fold that of the GG genotype. Importantly, among non-users of tobacco, the XRCC1 (GA+AA) variant emerged as the most significant determinant of an individual's susceptibility to leukoplakia (OR=3.5). In GSTM1 null individuals, tobacco consumption increased the risk of leukoplakia 21.3 fold. Similarly, XRCC1 A allele carriers and CCND1 A allele carriers who consumed tobacco were at a significantly high risk of developing leukoplakia (OR=11.8 and 14.9, respectively). Our study provides evidence that tobacco use in individuals harboring these polymorphic genotypes elevates the risk of oral leukoplakia and warrants further studies on gene-environment interactions to define the risk of malignant transformation of leukoplakia.

GSTM1 polymorphism is related to risks of nasopharyngeal cancer and laryngeal cancer: a meta-analysis

Background

Accumulating data have reported that GSTM1 polymorphism may be related to nasopharyngeal cancer (NPC) and laryngeal cancer (LC). This meta-analysis was performed to investigate the relationship between GSTM1 polymorphism and risks of NPC and LC.

Methods

Pubmed, Embase, and China National Knowledge Infrastructure (CNKI) databases were searched for potential articles. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the relationship of GSTM1 polymorphism with the risks of NPC and LC. I²>50% or P<0.05 indicates significant heterogeneity. When heterogeneity existed, the random-effects model was used to pool data, otherwise, the fixed-effects model was adopted. Publication bias was detected by Begg’s funnel plot and Egger’s regression. Quality of each study was evaluated by Newcastle-Ottawa Scale.

Results

Thirty-two eligible articles were included. Pooled outcome suggested the significant relationship of GSTM1 null genotype with increased risk of LC (OR =1.28, 95% CI =1.05–1.54). Compared with hospital-based (HB) population, GSTM1 null genotype was also related to increased risk of LC (OR =1.38, 95% CI =1.06–1.80). Positive relationship of GSTM1 null genotype with enhanced risk of NPC was observed (OR =1.43, 95% CI =1.26–1.63). A similar trend was also observed in the subgroup analysis by source of control (population-based [PB]: OR =1.39, 95% CI =1.18–1.63; HB: OR =1.52, 95% CI =1.22–1.89).

Conclusion

GSTM1 null genotype is related to increased risk of NPC and LC.

Cigarette smoking and the risk of head and neck cancer in the Japanese population: a systematic review and meta-analysis

OBJECTIVE

Although cigarette smoking is a well-established risk factor for head and neck cancer, the impact of smoking on head and neck cancer might vary among geographic areas. To date, however, no systematic review of cigarette smoking and head and neck cancer in the Japanese population has yet appeared.

METHODS

We conducted a systematic review of previous epidemiological studies for cigarette smoking and head and neck cancer among Japanese. Evaluation of associations was based on the strength of evidence ('convincing', 'probable', 'possible' or 'insufficient') and the magnitude of association ('strong', 'moderate', 'weak' or 'no association'), together with biological plausibility as previously evaluated by the International Agency for Research on Cancer. A meta-analysis was conducted to obtain summary estimates for the overall magnitude of association.

RESULTS

We identified five cohort studies and 12 case-control studies. Four of five cohort studies and 11 of 12 case-control studies showed a strong positive association between cigarette smoking and head and neck cancer. Nine of 12 studies indicated a dose-response relationship between cigarette smoking and the risk of head and neck cancer. Meta-analysis of 12 studies indicated that the summary relative risk for ever smokers relative to never smokers was 2.43 (95% confidence interval: 2.09-2.83). Summary relative risks for current and former smokers relative to never smokers were 2.68 (2.08-3.44) and 1.49 (1.05-2.11), respectively.

CONCLUSIONS

Cigarette smoking is a convincing risk factor for head and neck cancer in the Japanese population.

GSTM1 and GSTM5 Genetic Polymorphisms and Expression in Age-Related Macular Degeneration

PURPOSE

Previously, two cytosolic antioxidant enzymes, Glutathione S-transferase Mu 1 (GSTM1) and Mu 5 (GSTM5), were reduced in retinas with age-related macular degeneration (AMD). This study compared genomic copy number variations (gCNV) of these two antioxidant enzymes in AMD versus controls.

METHODS

Genomic copy number (gCN) assays were performed using Taqman Gene Copy Number Assays (Applied Biosystems, Darmstadt, Germany) in technical quadruplicate for both GSTM1 and GSTM5. Peripheral leukocyte RNA levels were compared with controls in technical triplicates. Statistical comparisons were performed in SAS v9.2 (SAS Institute Inc., Cary, NC).

RESULTS

A large percentage of patients in both AMD and age-matched control groups had no copies of GSTM1 (0/0). The mean gCN of GSTM1 was 1.40 (range 0-4) and 1.61 (range 0-5) for AMD and control, respectively (p = 0.29). A greater percentage of control patients had > 3 gCNs of GSTM1 compared with AMD, respectively (15.3% versus 3.0%, p = 0.004). The gCN of GSTM5 was 2 in all samples except one control sample. The relative quantification of GSTM1 and GSTM5 mRNA from peripheral blood leukocytes in patients showed significant differences in relative expression in AMD versus control (p < 0.05). Peripheral blood leukocyte mRNA and gCN were not significantly correlated (p = 0.27).

CONCLUSION

Since high copy numbers of GSTM1 are found more frequently in controls than in AMD, it is possible that high copy number leads to increased retinal antioxidant defense. Genomic polymorphisms of GSTM1 and GSTM5 do not significantly affect the peripheral blood leukocyte mRNA levels.

Glutathione S-transferase M1 gene polymorphism and laryngeal cancer risk: a meta-analysis

BACKGROUND AND OBJECTIVES

Studies investigating the association between glutathione S-transferase M1 (GSTM1) gene polymorphism and laryngeal cancer risk have reported conflicting results. The aim of the present study was to conduct a meta-analysis assessing the possible associations of GSTM1 gene polymorphism with laryngeal cancer risk.

METHODS

The relevant studies were identified through a search of PubMed, Embase, ISI Web of Knowledge and Chinese National Knowledge Infrastructure until May 2011 and selected on the basis of the established inclusion criteria for publications, then a meta-analysis was performed to quantitatively summarize association of GSTM1 polymorphism with laryngeal cancer susceptibility.

RESULTS

Seventeen studies were included in the present meta-analysis (2,180 cases and 2,868 controls). The combined results based on all studies showed that GSTM1 null genotype was associated with increased laryngeal cancer risk (OR = 1.17, 95% CI = 1.04∼1.31). When stratifying for race, GSTM1 null genotype exhibited increased laryngeal cancer risk in Caucasians (OR = 1.15, 95% CI = 1.01∼1.31), while no significant association was detected in Asians (OR = 1.25, 95% CI = 0.80∼1.96). In the subgroup analysis based on source of controls, significant associations were observed in the population-based studies (OR = 1.15, 95% CI = 1.01∼1.31) yet not in the hospital-based studies (OR = 1.25, 95% CI = 0.93∼1.67). Furthermore, in the subgroup analysis based on sample size, significant associations were also found in studies with at least 50 cases and 50 controls (OR = 1.15, 95% CI = 1.02∼1.30) but not in studies with fewer than 50 cases or 50 controls (OR = 1.46, 95% CI = 0.87∼2.46).

CONCLUSIONS

This meta-analysis supported that the GSTM1 gene polymorphism was associated with laryngeal cancer, particularly in Caucasians, and these associations varied in different subgroup, which indicated that population-based study with larger sample size was more appropriate in design of future study.

DNA methylation is associated with altered gene expression in AMD

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Evidence suggests oxidative stress plays a role in the disease. To assess the potential contribution of epigenetic regulation of antioxidant genes relevant to AMD pathogenesis, we evaluated DNA methylation, a tissue-specific genetic modulation that affects gene expression.

METHODS

Using the Infinium HumanMethylation27 Illumina platform, we performed DNA bisulfite sequencing to compare the methylation status in postmortem retina pigment epithelium (RPE)/choroid between patients with AMD and age-matched controls. Gene expression was assessed with the Affymetrix Exon Array. TaqMan gene expression assays were used for relative quantification (RT-PCR) confirmation of the expression array results: Glutathione S-transferase isoform mu1 (GSTM1) and mu5 (GSTM5) promoter methylation was confirmed by CpG island bisulfite pyrosequencing. To assess protein levels and localization, we used Western analysis, immunohistochemistry, and immunofluorescence with murine and human samples.

RESULTS

The mRNA levels of GSTM1 and GSTM5 were significantly reduced in AMD versus age-matched controls in RPE/choroid and neurosensory retina (NSR), which corresponded to hypermethylation of the GSTM1 promoter. mRNA and protein levels were decreased (RPE to a greater extent than NSR) in AMD postmortem samples, irrespective of age. Immunohistochemistry and immunofluorescence confirm the presence of the enzymes in the NSR and RPE.

CONCLUSIONS

Comparison of DNA methylation, together with mRNA levels, revealed significant differences between AMD versus normal retinas. The evidence presented suggests that GSTM1 and GSTM5 undergo epigenetic repression in AMD RPE/choroid, which may increase susceptibility to oxidative stress in AMD retinas.

Meta-analysis: glutathione-S-transferase allelic variants are associated with alcoholic liver disease

BACKGROUND

Only a minority of alcoholics develop alcoholic liver disease (ALD) and allelic variants within genes encoding glutathione-S-transferases (GST) have been associated with ALD vulnerability with controversial results.

AIM

To assess the effects of GST polymorphisms on ALD by means of a genetic association study and meta-analysis.

METHODS

We retrieved published studies on the relationship between allelic variants within GST genes and ALD by means of electronic database search. A meta-analysis was conducted in a fixed or random effects model. Calculations of odds ratios (OR) and their confidence intervals (CI), tests for heterogeneity of the results and sensitivity analysis, have been performed. A genetic association study comparing GSTM1, GSTT1 and GSTP1 genotype distribution among 279 alcoholics with or without ALD and 144 controls was also performed. Results  Fifteen previous studies were identified analysing the association of ALD with polymorphisms within GST genes. After meta-analysis, we found a significant association between the possession of the GSTM1 null allele and the presence of ALD (OR=1.43; 95% CI: 1.14, 1.78; P=0.002) among alcoholic patients. A significant association was also found for the possession of the GSTP1 Val/Val genotype and the presence of ALD (OR=2.04; 95% CI: 1.09, 3.80; P=0.03).

CONCLUSIONS

Our results suggest that, among alcoholics, carriers of GSTM1 null genetic variant or Val/Val genotype of Ile/Val GSTP1 polymorphism have an increased risk to suffer from alcoholic liver disease. The role of glutathione-S-transferase as a potential therapeutic target in alcoholic liver disease is reinforced.

GSTM1 and GSTT1 gene deletions and the risk for nasopharyngeal carcinoma in Han Chinese

Southern China is a major nasopharyngeal carcinoma-endemic region. Environmental factors and genetic susceptibility contribute to nasopharyngeal carcinoma development in this area. Polymorphic deletions of GSTM1 and GSTT1 genes involved in the detoxification of potentially carcinogenic agents may be a risk factor for nasopharyngeal carcinoma. To investigate the roles of genetic variations of GSTM1 and GSTT1 in nasopharyngeal carcinoma susceptibility in the Chinese population, we conducted a case-control study of 350 nasopharyngeal carcinoma cases and 622 controls. GSTM1 and GSTT1 deletion variants were genotyped by multiplex PCR assays. Logistic regression analysis was used to estimate odds ratios and 95% confidence intervals (95% CI). No significant association was observed for either GSTM1- or GSTT1-null genotype independently in the contribution to nasopharyngeal carcinoma risk. To explore possible joint effects of the GSTM1- and GSTT1-null polymorphisms with each other and with other risk factors for nasopharyngeal carcinoma, we examined the association between each combined genotype and the risk for nasopharyngeal carcinoma stratified by gender and EBV replication status. We found that individuals who carried GSTM1/GSTT1-double null genotype had a higher risk for nasopharyngeal carcinoma in the male population (odds ratio, 1.76; 95% confidence interval, 1.04-2.97; P = 0.03); however, this was not significant after correction for multiple comparisons. No statistical difference was found between cases and controls in females and the subpopulation positive for immunoglobulin A antibodies to EBV capsid antigen for combined genotypes. Our results suggest that the GSTM1/GSTT1-double null genotype may be a risk factor for nasopharyngeal carcinoma among males in southern China, but this result warrants confirmation in other studies.

CYP1A1, mEH, and GSTM1 Polymophisms and Risk of Oral and Pharyngeal Cancer: A Spanish Case-Control Study

Background. Genetic polymorphisms of drug metabolizing enzymes involved in the detoxification pathways of carcinogenic substances may influence cancer risk. Methods. Case-control study that investigates the relationship between CYP1A1 Ile/Val, exon 4 mEH, and GSTM1 null genetic polymorphism and the risk of oral and pharyngeal cancer examining the interaction between these genes, tobacco, and alcohol. 92 incident cases and 130 consecutive hospital-based controls have been included. Results. No significant associations were found for any of the genotypes assessed. The estimated risk was slightly elevated in subjects with the wild type of the mEH gene and the null GSTM1 genotype. For exon 4 mEH heterozygous polymorphism, the risk was slightly lower for heavy smokers than for light smokers. The inverse association was observed for the GSTM1 null genotype. Conclusions. The results suggest that exon 4 mEH and GSTM1 null polymorphisms might influence oral and pharyngeal cancer.

Meta-analysis and pooled analysis of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers: a HuGE-GSEC review

The association of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers was assessed through a meta-analysis of published case-control studies and a pooled analysis of both published and unpublished case-control studies from the Genetic Susceptibility to Environmental Carcinogens database (http://www.upci.upmc.edu/research/ccps/ccontrol/index.html ). Thirty publications used in the meta-analysis included a total of 7783 subjects (3177 cases and 4606 controls); 21 datasets, 9397 subjects (3130 cases and 6267 controls) were included in the pooled analysis. The GSTM1 deletion was 2-fold more likely to occur in African American and African cases than controls (odds ratio: 1.7, 95% confidence interval: 0.9-3.3), although this was not observed among whites (odds ratio: 1.0, 95% confidence interval: 0.9-1.1). The meta-analysis and pooled analysis showed a significant association between oral and pharyngeal cancer and the CYP1A1 MspI homozygous variant (meta-ORm2/m2: 1.9, 95% confidence interval: 1.4-2.7; Pooled ORm2m2: 2.0, 95% confidence interval: 1.3-3.1; ORm1m2 or [infi]m2m2: 1.3, 95% confidence interval: 1.1-1.6). The association was present for the CYP1A1 (exon 7) polymorphism (ORVal/Val: 2.2, 95% confidence interval: 1.1-4.5) in ever smokers. A joint effect was observed for GSTM1 homozygous deletion and the CYP1A1 m1m2 variant on cancer risk. Our findings suggest that tobacco use and genetic factors play a significant role in oral and pharyngeal cancer.

Association of genetic polymorphisms in glutathione S-transferases and susceptibility to head and neck cancer

Polymorphism in glutathione S-transferase (GST) genes (GSTM1, GSTT1 and GSTP1) and interaction with environmental factors such as tobacco (smoking or chewing) and alcohol on susceptibility to head and neck squamous cell carcinoma (HNSCC) was studied in a case-control study. The study group consisted of 175 patients suffering from HNSCC and 200 age matched healthy controls. Statistical analysis showed an increase in risk to HNSCC in the patients with null genotype of GSTM1 (OR: 2.02; 95% CI: 1.32-3.10; P=0.001) or GSTT1 (OR: 1.66; 95% CI: 1.02-2.69; P=0.04), though the risk was not found to be significant when adjusted for age, sex, smoking, tobacco chewing or alcohol use by multivariate logistic regression model. Our data further showed that combination of deletion genotypes of GST (GSTM1 and GSTT1) confer an even higher risk of HNSCC. Interestingly, GSTP1 wild type genotype in combination with GSTM1 null or GSTT1 null genotype increased susceptibility for HNSCC (OR: 2.49 and 2.75, respectively). Likewise a much greater risk for HNSCC was observed in the patients carrying a genotype combination of GSTM1 null, GSTT1 null and GSTP1 (Ile/Ile) (OR: 4.47; 95% CI: 1.62-12.31; P=0.002). Our data have further provided evidence that tobacco chewing and alcohol consumption are the important risk factors for HNSCC. The interaction between tobacco chewing and null genotype of GSTM1 or GSTT1 resulted in about 3.5- and 2.2-fold increase in the risk respectively in the patients when compared to those not chewing tobacco. Alcohol use resulted in more than 4-fold increase in the risk in the patients with null genotype of GSTM1 as compared to those who are non-drinkers. Alcohol consumption also increased the risk (approx. 3-fold) in the cases with null genotype of GSTT1, though the association was not found to be significant when compared to non-drinkers. Our data have provided evidence that GST polymorphism modifies the susceptibility to HNSCC and have further demonstrated importance of gene-environment interaction in modulating the risk to HNSCC.

Polymorphisms of CYP1A1 and GSTM1 genes and susceptibility to oral cancer

PURPOSE

Oral cancer is the fifth most common form of cancer in the world and comprises 6.5% of all cancer deaths. Since one of the major risk factors for oral cancer is tobacco use, we hypothesized that polymorphic genes coding for tobacco carcinogen-metabolizing enzymes may play a role in oral cancer susceptibility.

MATERIALS AND METHODS

To investigate the association between polymorphisms of the CYP1A1 and GSTM1 genes and risks for oral squamous cell carcinoma (OSCC) in the Korean population, the prevalence of the CYP1A1 Mspl and GSTM1 null polymorphisms were examined in 72 patients with histologically confirmed primary OSCC, as well as in 221 healthy control subjects.

RESULTS

A significant risk increase for oral cancer was observed among subjects with the homozygous CYP1A1 (m2/m2) genotype (OR=3.8, 95% CI=1.9-7.7), but not the GSTM1 null genotype (OR=0.7, 95% CI=0.4-1.3). Risk for oral cancer was significantly increased in subjects with the homozygous CYP1A1 (m2/m2)genotype, regardless of smoking history (smokers; OR=4.4; 95% CI=1.2-16.3; non- smokers OR=4.9; 95% CI=1.9-12.5). Using the potentially most protective genotype GSTM1 (+)/CYP1A1 [(m1/m1)+ (m1/m2)] as the reference group, an increased risk for oral cancer was observed among subjects with the GSTM1 (+)/ CYP1A1 (m2/m2) (OR= 2.0, 95% CI=0.8-5.2), and GSTM1 (-)/ CYP1A1 (m2/m2) (OR=4.9, 95% CI=1.5-15.5) genotypes (p < 0.009, (chi2 trend test).

CONCLUSION

Our results suggest that individuals with a genotype of CYP1A1 (m2/m2) and GSTM1 (-) are highly susceptible for OSCC and that the CYP1A1 (m2/m2) genotype is closely associated with increased risk of OSCC in Koreans.

Relation of glutathione S-transferase genotypes (GSTM1 and GSTT1) to laryngeal squamous cell carcinoma risk

The purpose of the present study was to investigate GSTM1 and GSTT1 genotypes by using multiplex polymerase chain reaction (PCR) in patients with laryngeal squamous cell carcinoma (LSCC). The genotypes of 110 patients with LSCC and of 197 healthy subjects as the control group were determined by PCR analysis for GSTM1 and GSTT1 genes. Results showed that frequencies of GSTM1-null, GSTT1-null, and both GSTs-null genotypes were 51.8, 30, and 16.4%, respectively, in the patients with LSCC and 37.6, 15.7, and 5.6% in the control group. There was a significant difference between the genotype distributions of all GSTs in patients and in control groups (P < 0.05). The results support the hypothesis that null genotypes of GSTM1 and GSTT1 can reduce detoxification capacity of GSTs as members of the xenobiotic enzyme system. GSTM1-null, GSTT1-null, and both GSTs-null genotypes were more common in the patients with LSCC than in the control group. Patients with both GSTs-null genotypes had the highest risk for supraglottic LSCC in the early period, even if they were light-to-medium smokers. Investigation and determination of the genetic basis of LSCC may contribute to detection of risk groups and to prevent LSCC in the population.

GSTT1 and GSTM1 allelic polymorphisms in head and neck cancer patients from Italian Lazio Region

BACKGROUND

The association between head and neck squamous cell carcinoma (HNSCC) and allelic variants of glutathione S-transferase M1 (GSTM1) and -T1 (GSTT1) is currently controversial. The present study investigates the prevalences of GSTT1 and GSTM1 polymorphism in a cohort of 100 head and neck cancer patients, 100 healthy donors and 200 controls with non-neoplastic head and neck diseases from Italian Lazio Region.

METHODS

The patients with benign head and neck pathologies, as well as the healthy donors were matched for age, sex, cigarette smoke (yes/no) and alcohol consumption (yes/no). Molecular definition of GSTT1 and GSTM1 genotype has been performed by means of allele-specific PCR technique.

RESULTS

A significant association between head and neck cancer and GSTM1 null genotype was observed both considering benign disease controls (p=0.001, OR=2.613; 95% C.I.=1.48-4.62), and healthy donors (p=0.0003, OR=3.35; 95% C.I. 1.69-6.67) while no significant association was found with GSTT1 null genotype (p>or=0.14). No interactive association was observed when combining the different genotypes of the two polymorphisms. These results were confirmed after correction for daily number of cigarettes and period of tobacco exposure.

CONCLUSIONS

The present study confirms a role for genetic alterations of GSTM1 detoxifying enzyme as a risk factor for the development of HNSCC in patients from the Italian Lazio Region, independently of age, sex and other confounding variables.

Meta-analysis of glutathione S-transferase M1 genotype and risk toward head and neck cancer

BACKGROUND

We sought to evaluate the estimated risk of GSTM1 null genotype and squamous cell carcinoma of the head and neck (SCCHN).

METHODS

The studies done so far for GSTM1 null genotype as a risk factor associated with head and neck cancer are not conclusive and have shown conflicting results. A meta-analysis has been carried out on 22 case-control studies collected from the literature. Precision of the risk estimate and presence of publication bias in those studies are also evaluated by funnel plot analysis.

RESULTS

A total of 3527 cases and 4211 controls constitute the subjects of meta-analysis. The principal outcome measured was the odds ratio (OR) for the risk of head and neck cancer. Pooling the studies together, the OR was 1.50 (95% confidence interval [CI], 1.21-1.87). When stratified according to Asians and Caucasians, the OR increased in the Asians (OR, 1.93; 95% CI, 1.29-2.90), suggesting that the risk is more pronounced in Asians. However, a substantial amount of publication bias is also associated with studies conducted on the Asian population.

CONCLUSION

A review of the 22 case-control studies for risk of SCCHN and GSTM1 null genotype indicate that greater attention should be paid to designing future studies so that a more precise risk estimate can be achieved.

Glutathione S-transferase T1 null polymorphism and the risk for head and neck cancer

CONCLUSIONS

Inter-regional differences in the distribution of genetic polymorphisms in glutathione S-transferases (GSTs) exist, which may have significant effect on the outcome of other GST polymorphism studies. The GSTT1 null genotype appears to be involved in modulation of the risk for head and neck squamous cell carcinoma (HNSCC).

BACKGROUND

The risk of HNSCC is strongly associated with smoking of cigarettes and consumption of alcohol, resulting in a load of toxins/carcinogens. Detoxification of such exogenous harmful compounds often occurs by phase II enzymes such as GSTs. Proper functioning of these enzymes may be deficient due to the presence of particular genetic polymorphisms in these GSTs, and this may increase the risk for HNSCC. We compared the GSTT1, GSTM1 and GSTP1 genotype frequencies in two groups of healthy blood donors, collected from different but adjacent regions in the Netherlands, with those of a group of patients with HNSCC.

SUBJECTS AND METHODS

The GSTM1,GSTT1 and GSTP1 genotype frequencies in two Dutch Caucasian control populations (n = 207 and n = 285) from different but adjacent geographical regions (Maastricht and Nijmegen; distance, 125 km) and 185 patients with HNSCC from the Maastricht region were determined by PCR-related methods.

RESULTS

For the occurrence of the GSTT1 null genotype we found a significant difference (p=0.003) between the two control groups (20.3% vs 33.0% null genotype in the Nijmegen and Maastricht control groups, respectively). Since the HNSCC patients were collected from the Maastricht area, comparison with the Maastricht controls reveals a significant difference for GSTT1 null rates, which are lower in patients vs controls (OR = 0.49, CI = 0.32-0.76).

CYP1A1, CYP2D6, CYP2E1, NAT2, GSTM1 and GSTT1 polymorphisms or their combinations are associated with the increased risk of the laryngeal squamous cell carcinoma

Polymorphisms in the selected genes controlling carcinogen metabolism (CYP1A1, CYP2D6, CYP2E1, NAT2, GSTM1, GSTT1) considered separately or in different combinations, were investigated for an association with tobacco smoke-associated squamous cell carcinoma (SCC) of the larynx. The case-control study was performed in 289 patients with laryngeal SCC and in 316 cancer-free controls; all were Caucasian males from the same region of Poland and current tobacco smokers. The DNA samples were genotyped using PCR-RFLP and multiplex PCR. The variants' frequencies in both groups were compared; odds ratios and their 95% confidence intervals were calculated by logistic regression analyses. The CYP1A1*1/*4, CYP2D6*4/*4, NAT2*4/*6A genotypes, as well as the CYP1A1*4, CYP2D6*4 and NAT2*4 alleles, were found at significantly higher frequencies in cases than in controls indicating their role as "risk-elevating" factors in laryngeal SCC. Combined genotypes, characterized by the presence of the "risk-elevating" variants at more than one locus, often occurred together with the null variant of the GSTM1 gene and homozygous XPD A/A (Lys751Gln, A35931C) genotype. Furthermore, we identified some "protective" variants, found more frequently in controls than in cases, i.e. the NAT2*6A/*6A and NAT2*5B/*6A genotypes. A distribution of "risk" or "protection" genotypes/alleles seems to be connected with age as an occurrence or risk genes was more frequent in the group of "young" cases (< or = 49 years). Accumulation of certain alleles or genotypes of the CYP1A1, NAT2, GSTM1 and XPD seems to be associated with either increased or decreased risk to develop laryngeal SCC. Therefore, polymorphisms in these genes may play a role in the laryngeal cancer etiology.

Glutathione S-transferase M1, T1, and P1 gene polymorphism in laryngeal squamous cell carcinoma

PURPOSE

To investigate the influence of the glutathione S-transferase (GST) M1, T1, and P1 genotypes on the laryngeal squamous cell carcinoma risk.

MATERIAL AND METHODS

The study group consisted of 42 white patients with laryngeal squamous cell carcinoma (39 of them were male, mean age: 53, range: 37-67 and 3 of them were female, mean age: 47, range: 32-55) and 89 control subjects (nonsmokers = 47, smokers = 42) (58 male and 31 female, mean age: 51, range: 30-72). DNA samples were isolated from blood samples using high pure polymerase chain reaction (PCR) Template Preparation Kit. The detection of GST T1, GST M1, and P1 polymorphisms were detected by using real-time PCR.

RESULTS

Gene polymorphisms at GST M1 and P1 were not significantly different in patient and control groups. However, GST T1 null type significantly increased in laryngeal cancer patients when compared with the nonsmoking controls (P =.04).

CONCLUSIONS

There was a significant association between GST T1 null genotype and laryngeal squamous cell carcinoma. However the potential role of GSTs as markers of susceptibility to laryngeal carcinoma needs further studies in a larger number of patients.

Polymorphisms of GSTT1 and related genes in head and neck cancer risk

BACKGROUND

Glutathione S-transferase T1 detoxifies some environmental carcinogens while activating others and is deleted in 15% to 38% of humans. We sought to determine whether GSTT1 genotype and genotypes of several related genes are associated with risk of squamous cell carcinoma of the head and neck (HNSCC).

METHODS

Somatic genotypes for GSTT1, GSTM1, GSTP1, and CYP1A1 were determined in 283 individuals with HNSCC and 208 population-based controls.

RESULTS

The OR for presence of GSTT1 was 1.6 (CI, 1.1-2.5, p = 0.03). HNSCC risk was not associated with GSTM1 null genotype, the presence of the GSTP1 Val/Val genotype, or the Val/Val homozygous genotype for CYP1A1. Stratified analysis revealed disparate ORs for women (OR, 3.0; CI, 1.5-6.3) and men (OR, 1.2; CI, 0.7-2.1) for the presence of GSTT1.

CONCLUSIONS

In this population, the presence of GSTT1 gene was associated with a significant increase in the risk of HNSCC. This association was particularly robust in women.

Glutathione S-transferase M1 or T1 null genotype as a risk factor for developing multiple primary neoplasms in the upper aero-digestive tract, in Indian males using tobacco

In this study conducted amongst Indian male tobacco users with upper aero-digestive tract (UADT) squamous carcinoma, 30 patients with multiple primary neoplasms (MPN) were compared with 28 age and sex matched patients with a single primary neoplasm (SPN) for various environmental factors (form of tobacco use, alcohol, radiotherapy for index cancer) and genetic parameters (family history of UADT cancers and GSTT1/GSTM1 genotype). The GSTM1/T1 null genotype, seen in 60% patients with MPN versus 33% patients with SPN (P=0.03) had an odds ratio of 3.7 [CI=1.14-11.99; P=0.03] for developing MPN. Tobacco use in the form of smoking with or without chewing, as opposed to only chewing, and regular alcohol intake were the two other factors with almost three fold increased risk for the development of MPN, although, the effect was not statistically significant. All three patients with a family history of UADT cancer developed MPN, suggesting an inherited predisposition.

GlutathioneS-transferaseM3 (A/A) genotype as a risk factor for oral cancer and leukoplakia among Indian tobacco smokers

Polymorphism in glutathione S-transferase (GST) genes, causing variations in enzyme activities, may influence susceptibility to oral cancer and leukoplakia in smokers and/or smokeless tobacco users. In this case-control study consisting of 109 leukoplakia and 256 oral cancer patients and 259 controls, genotype frequencies at GSTM1, GSTT1, GSTM3 and GSTP1 loci were determined by polymerase chain reaction-restriction fragment length polymorphism methods and analyzed by multiple logistic regression to determine the risks of the diseases. There were no significant differences in the distributions of GSTM1, GSTM3 and GSTT1 genotypes in patients and controls when all individuals were compared. In contrast, frequencies of ile/ile genotype at codon 105 and variant val-ala haplotype of GSTP1 was significantly higher (OR = 1.5; 95% CI = 1.0-2.0) and lower (OR = 1.4; 95% CI = 1.0-1.9) in oral cancer patients compare to controls, respectively. The impacts of all genotypes on risks of oral cancer and leukoplakia were also analyzed in patients with different tobacco habits and doses. Increased risks of cancer and leukoplakia were observed in tobacco smokers with GSTM3 (A/A) genotype (OR = 2.0, 95% CI = 1.0-4.0; OR = 2.0, 95% CI = 1.0-4.4, respectively). So, GSTM3 (A/A) genotype could become one of the markers to know which of the leukoplakia would be transformed into cancer. Heavy tobacco chewing (> 124 chewing-year) increased the risk of cancer in individuals with GSTT1 homozygous null genotype (OR = 3.0; 95% CI = 1.0-9.8). Furthermore, increased lifetime exposure to tobacco smoking (> 11.5 pack-year) increased the risk of leukoplakia in individuals with GSTM1 homozygous null genotype (OR = 2.4; 95% CI = 1.0-5.7). It may be suggested that polymorphisms in GSTP1, GSTM1, GSTM3 and GSTT1 genes regulate risk of cancer and leukoplakia differentially among different tobacco habituals.

Epoxide hydrolase genotype and orolaryngeal cancer risk: interaction with GSTM1 genotype

The human microsomal epoxide hydrolase (EH) gene contains polymorphic alleles which are associated with altered EH activity and may be linked to increased risk for tobacco-related cancers. The objective was to examine the role of EH polymorphisms in orolaryngeal cancer risk. The prevalence of the EH codons 113 and 139 polymorphisms were examined in 81 African American and 142 Caucasian incident orolaryngeal cancer patients and 335 controls frequency-matched on age, sex, and race. In Caucasians, a significant risk increase was observed for subjects with the EH(113Tyr) variant (OR=2.1, 95% CI=1.1-4.0) and predicted high-activity EH genotypes in heavy-smokers (>or=35 pack-years; OR=3.4, 95% CI=1.2-9.6). A significant association between predicted high EH activity genotypes and orolaryngeal cancer risk was observed in Caucasian subjects with the GSTM1 null (OR=3.5, 95% CI=1.3-9.3) but not GSTM [+] (OR=0.9, 95%CI=0.4-2.1) genotype. These results suggest that EH polymorphisms play an important role in risk for orolaryngeal cancer in Caucasians.

Laryngeal cancer risk in Caucasians is associated with alcohol and tobacco consumption but not modified by genetic polymorphisms in class I alcohol dehydrogenases ADH1B and ADH1C, and glutathione-S-transferases GSTM1 and GSTT1

OBJECTIVE

Alcohol and tobacco consumption are recognized risk factors for upper aerodigestive tract tumours, however individual susceptibility to these environmental factors varies. As part of the Rhein-Neckar Larynx-case-control study, this study investigated the potential risk-modifying effect of genetic polymorphisms in enzymes involved in ethanol and tobacco carcinogen metabolism for laryngeal cancer in Germany.

METHODS

Two hundred and forty-five cases and 251 population-based controls, matched by age and gender, were genotyped for genetic polymorphisms in ADH1B, ADH1C, GSTM1 and GSTT1, using genomic DNA isolated from peripheral lymphocytes and employing PCR and PCR/restriction fragment length polymorphism-based methods.

RESULTS

Neither the putative risk genotypes ADH1B*2/*1 (OR 0.86, 95% confidence interval (CI): 0.41-1.82) or ADH1C*1/*1 (OR 1.06, CI 0.7-1.62) nor GSTM1 null (OR 0.94, CI 0.62-1.42) or GSTT1 null (OR 1.34, CI 0.74-2.42) were associated with an overall increased risk for laryngeal cancer. Stratified analyses were carried out to determine the gene-environment interaction in relation to laryngeal cancer risk. However, ADH1B or ADH1C genotypes did not markedly modify the risk observed after stratification by alcohol consumption, and stratification by cumulative smoking exposure (in packyears) did not show an association of GSTM1 or GSTT1 genotype with laryngeal carcinoma either.

CONCLUSION

The lack of risk modification by the studied genotypes emphasizes the importance of environmental exposure to tobacco smoke and alcohol as major risk factors for laryngeal cancer in the German study population.

Biomonitoring of tobacco smoke carcinogenicity by dosimetry of DNA adducts and genotyping and phenotyping of biotransformational enzymes: a review on polycyclic aromatic hydrocarbons

In this review article, we summarize the data on tobacco smoke carcinogenicity in relation to DNA adduct dosimetry and genotyping and phenotyping of biotransformational enzymes. A major class of carcinogens, polycyclic aromatic hydrocarbons, present in substantial quantities in tobacco smoke, is discussed. The historical background and an overview of the metabolic pathways are given. The epidemiological and biological data in particular on dosimetry of the representative DNA adducts and genotyping and phenotyping of the respective activating and detoxifying enzymes are presented. The salient findings are highlighted, the uncertainties are underlined and, finally, recommendations for future research are made.

Mutagen sensitivity of nasopharyngeal cancer patients

Primary nasopharyngeal carcinomas (NPCs) may be of various types, including squamous cell carcinomas, undifferentiated carcinomas, and lymphoepitheliomas. Tumor initiation has been linked to the Epstein-Barr virus and, in some geographical regions, to alimentary factors. Possible hereditary components for the appearance of NPCs have not yet been clearly identified. In this study, genetic sensitivity to the genotoxic effects of carcinogenic xenobiotics as an endogenous risk factor of tumor initiation was investigated. The single cell microgel electrophoresis assay was used to quantify chemically-induced DNA damage in lymphocytes of 30 NPC patients and 30 non-tumor donors. The xenobiotics investigated were N'-nitrosodiethylamine, sodium dichromate, and nickel sulphate, with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and dimethyl sulfoxide (DMSO) as positive and negative controls, respectively. The extent of DNA migration in the solvent control cultures was not significantly different between the two groups (1.2+/-0.5 mean Olive tail moment and standard deviation of 30 individuals for NPC patients; 1.1+/-0.4 for non-tumor donors). With constant exposure and electrophoretic conditions, genotoxic effects of varying degrees were induced by the different xenobiotics in tumor and non-tumor patients (nickel sulphate: 7.1+/-2.5 for NPC patients and 5.9+/-1.6 for non-tumor donors; sodium dichromate: 18.1+/-5.3 for NPC patients and 16.2+/-5.4 for non-tumor donors; MNNG: 47.8+/-13.3 for NPC patients and 52.7+/-13.6 for non-tumor donors). Only N'-nitrosodiethylamine proved to induce significantly more DNA migration in lymphocytes of tumor patients (9.8+/-3.1) as compared to non-tumor patients (8.2+/-2.3). Although for sodium dichromate the degree of DNA migration did not significantly differ, variability in migration patterns proved to be lower in the tumor group. Mutagen sensitivity of NPC patients was shown to be elevated for a selected xenobiotic, whereas a general elevation of DNA fragility was not present. Further studies on mutagen sensitivity as an endogenous risk factor influencing the susceptibility of patients at the time of first diagnosis of nasopharyngeal carcinomas are warranted.

Genetic deletions of glutathione-S-transferase as a risk factor in squamous cell carcinoma of the larynx: a preliminary report

PURPOSE

To test whether genetic deletions of glutathione-S-transferase (GST) are associated with squamous cell carcinoma (SCC) of the larynx. GST are a group of detoxifying enzymes that may help reduce the risk of developing cancer in response to environmental carcinogens. Polycyclic aromatic hydrocarbons, found in high concentration in cigarette smoke, are known carcinogens especially for SCC of the larynx. Individuals with absolute or relative deficiency of the GST enzyme system may therefore be at a higher risk of developing laryngeal carcinoma.

MATERIALS AND METHODS

Genotyping for GST-M1 and GST-T1 was performed using polymerase chain reaction (PCR) assay on fresh frozen tissue specimens of 20 patients with SCC of the larynx and on 20 control subjects with a similar smoking history. Because this assay results in the absence of a PCR product in individuals expressing the GST-M1/GST-T1 null genotype, oligonucleotide primers that amplify a portion of the albumin gene were included in a multiplex PCR as a positive control for DNA quality and PCR conditions. The chi-square test was used for statistical analysis.

RESULTS

GST-M1 gene was deleted in 80% of patients with laryngeal SCC and in 50% of control subjects (P <.05). No statistically significant difference was observed in the incidence of GST-T1 gene deletion in patients with SCC of the larynx and control subjects.

CONCLUSION

GST-M1 gene deletion was significantly associated with SCC of the larynx and may produce a risk for this particular disease.

Genetic polymorphisms in head and neck cancer risk

OBJECTIVE

To assess whether genetic polymorphisms implicated as risk factors for other tobacco-associated malignancies are associated with altered risk of head and neck squamous cell carcinoma.

DESIGN

Case-control study.

SUBJECTS

One hundred sixty patients with head and neck squamous cell carcinoma recruited from a university-based head and neck oncology clinic and 149 population-based controls.

METHODS

Genotyping of the CYP1A1 (Ile462Val), GSTM1 (null), GSTP1 (Ile105Val), GSTT1 (null), and P53 (Arg72Pro) genes was performed by polymerase chain reaction-based techniques on DNA prepared from peripheral blood. In addition, a questionnaire was used to collect demographic information from each subject.

RESULTS

Cases were significantly older (p <.0001) and had significantly greater tobacco use (p <.0001) and were more likely to be male (p <.0001) than were control subjects, thus confirming known risk factors for this disease. When cases and controls were compared by simple chi-square analysis, only the frequency of CYP1A1 (Ile462Val) polymorphism was significantly different between cases and controls (OR =.42; 95% CI =.18-.99; p <.04). However, with a logistic regression model to control for known risk factors, we were unable to demonstrate a significant association with head and neck cancer for any of the polymorphisms tested, including CYP1A1.

CONCLUSIONS

This population fails to identify a relationship between the above-mentioned polymorphisms and head and neck cancer.

Metabolizing enzyme genotype and risk for upper aerodigestive tract cancer

Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of upper aerodigestive tract cancer. It has been suggested that such polymorphisms may be linked to cancer susceptibility. Using a case-control molecular epidemiologic approach, the association between many of these genetic polymorphisms and susceptibility to upper aerodigestive tract cancer has been investigated in numerous studies. In this review, we summarize the findings of these studies, analyzing potential associations with upper aerodigestive tract cancer risk in terms of gene:environment interactions, genotype-induced functional defects in enzyme activity and/or expression, and the influence of race on these associations.

Influence of glutathione S-transferase M1 and T1 genotypes on larynx cancer risk among Korean smokers

Glutathione S-transferase (GST) isoenzymes are involved in the detoxification of major carcinogens present in tobacco smoke. It is thus conceivable that deficiency in GST activity due to homozygous deletions of the GSTM1 and GSTT1 genes (the null genotypes) may modulate susceptibility to smoking-induced cancers. The influence of the GSTM1 and GSTT1 null genotypes on larynx cancer risk among the Korean population were evaluated using peripheral blood DNA from 82 larynx cancer patients and 63 healthy controls, all of whom were male current smokers. Increased larynx cancer risk was related to the GSTM1 null genotype (odds ratio (OR)=3.53, 95% confidence interval (CI)=1.27-9.83). The OR associated with the GSTT1 null genotype was also increased, but did not reach statistical significance (OR=1.83, 95% CI=0.70-4.79). Individuals lacking both the GSTM1 and GSTT1 genes were at a significantly higher risk for larynx cancer than individuals with both genes present (OR=4.04, 95% CI=1.33-12.30). These data confirm that the GSTM1 null genotype is an important risk modifier for larynx cancer among Korean smokers and combined GSTM1 and GSTT1 null genotypes could be a useful predictor of genetic susceptibility to larynx cancer.

Comparing the genotoxic sensitivities of human peripheral blood lymphocytes and mucosa cells of the upper aerodigestive tract using the Comet assay

Carcinogenesis in the upper aerodigestive tract is influenced by multiple factors. Besides tobacco and alcohol consumption, specific pollutants such as phthalates, nitrosamines, and polycyclic aromatic carbohydrates may be important in tumor initiation. Genetic factors related to mutagen sensitivity and DNA repair capacity also play a role. The aim of this study was to investigate whether human peripheral blood lymphocytes and mucosal epithelium of the upper aerodigestive tract, the target for volatile and liquid xenobiotics, are equally sensitive to genotoxic agents. The Comet assay was used to detect for DNA damage induced by genotoxic agents in mucosal epithelial cells and peripheral blood lymphocytes of 60 volunteers. Mucosa was harvested from larynx, oropharynx, and inferior nasal turbinates. Xenobiotics investigated were dibutylphthalate (DBP), diisobutylphthalate (DiBP), N'-nitrosodiethylamine (NDELA), benzo[a]pyrene (B[a]P), and N'-methyl-N'-nitro-N-nitrosoguanidine (MNNG). DBP, DiBP, B[a]P, NDELA and MNNG induced a significant increase in DNA migration in both cell populations. Peripheral blood lymphocytes were more sensitive than mucosal cells to DBP and DiBP, but not to NDELA and B[a]P. The correlation, in terms of DNA migration, between lymphocytes and mucosal cells among volunteers was relatively poor. Based on the poor correlation in response between the two cell types, the sensitivity of peripheral blood lymphocytes to genotoxic agents appears to be a poor predictor of sensitivity in the target cells of the upper aerodigestive tract. Further attention should be focused on intra-individual mutagen sensitivities and inter-individual genetic differences as regards susceptibility to upper aerodigestive tract cancer.

Comparison of GSTM polymorphisms and risk for oral cancer between African-Americans and Caucasians

Two members of the mu class of glutathione S-transferase (GST) genes, GSTM1 and GSTM3, have polymorphic alleles which have been associated with altered levels of GST mu protein expression and may be linked to increased risk for several tobacco-related cancers. Oral cancer is a tobacco-related disease that affects African-American men at a significantly higher incidence than Caucasian men. To examine the potential role of GSTM polymorphisms in risk for oral cancer in African-Americans and Caucasians, the prevalences of the GSTM1 null and GSTM3 intron 6 polymorphisms were examined in 63 African-American and 101 Caucasian patients with histologically confirmed primary oral cancer, as well as in 133 African-American and 213 Caucasian matched control subjects. In African-Americans, the odds ratio for oral cancer associated with the GSTM1 (0/0) genotype was 3.1 [95% confidence interval (CI) = 1.1-8.5], with the association between the GSTM1 (0/0) genotype and oral cancer risk strongest in heavy smokers [i.e. > 24 pack-years; odds ratio (OR) = 5.4, 95% CI = 1.2-24]. Using the potentially most protective GSTM1 [+]/GSTM3 (B/B) genotype as the reference group, increased risk for oral cancer was observed in African-Americans with the GSTM1 [+]/GSTM3 [(A/A) + (A/B)] (OR = 2.2, 95% CI = 0.82-6.0), GSTM1 (0/0)/GSTM3 (B/B) (OR = 4.3, 95% CI = 1.1-16), and GSTM1 (0/0)/GSTM3 [(A/A) + (A/B)] (OR = 6.6, 95% CI = 1.2-38) genotypes (P < 0.01, trend test). No significant associations were observed between GSTM genotype and oral cancer risk in Caucasians. These results suggest that the GSTM1 null and GSTM3 intron 6 polymorphisms play an important role in risk for oral cancer among African-Americans and implicates the mu class of GSTs as important tobacco carcinogen detoxifying enzymes in this population.

Genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and oral cavity cancer

Both genetic and environmental factors are involved in the development of cancer. Oral cavity cancer has been reported to be epidemiologically associated with tobacco and alcohol consumption. We examined genetic polymorphisms of the glutathione-S-transferase (GST) M1/T1, cytochrome P-450 (CYP) 1A1/2E1 and aldehyde dehydrogenase 2 (ALDH2) genes in 92 Japanese patients with oral cavity cancer and 147 unrelated non-cancer Japanese controls. There was a significant association between cigarette smoking and cancer risk but no significant association between alcohol consumption and cancer risk. The frequency of the GSTM1 null genotype was significantly higher in cancers (58.7%) compared with controls (46. 3%). However, there were no significant differences between controls and patients with oral cavity cancer in the polymorphisms of the GSTT1, CYP1A1, CYP2E1 and ALDH2 genes. From statistical evaluation on various combinations of genotypes, we did not observe any gene combinations associated with cancer risk. There were also no genetic polymorphisms associated with increased risk of oral cavity cancer among smokers and drinkers. These results imply that the GSTM1 null genotype has a weak correlation, but another 4 genetic polymorphisms are unlikely to be associated, with oral cavity cancer among Japanese.

Drug metabolism polymorphisms as modulators of cancer susceptibility

Recently, several molecular genetic bases of polymorphic enzyme activities involved in drug activation and detoxification have been elucidated. Many molecular epidemiology studies based on these premises have sought to gather information on the association of genetically determined metabolic variants with different risks of environmentally induced cancer. While rare alterations of tumor suppressor genes dramatically raise cancer risk for the single affected subjects, far more common and less dramatic differences in genes encoding for drug metabolism enzymes can be responsible for a relatively small, but rather frequent increase of cancer risk at the population level. This increase could be especially important in specific cases of occupational, pharmacological or environmental exposure. Examination of the current literature reveals that the most extensively investigated metabolic polymorphisms are those of P450 1A1 and P450 2D6 cytochromes, glutathione S-transferases (GSTs; M1 and, to a lesser extent, M3, P1 and T1) and N-acetyltransferases (NATs; NAT1 and NAT2). Making reference to these enzymes, we have assayed the current knowledge on the relations among polymorphisms of human xenobiotic-metabolizing enzymes and cancer susceptibilities. We have found intriguing models of susceptibility toward different types of cancer. We have reviewed and commented these models on light of the complex balance among different enzyme activities that, in each individual, determines the degree of each cancer susceptibility. Moreover, we have found techniques of molecular genetic analysis, more suitable than previous ones on phenotypic expression, now allowing better means to detect individuals at risk of cancer. According to the models presently available, a systematic screening of individuals at risk seems to make sense only in situations of well defined carcinogenic exposures and when performed by the polymorphism analysis of coordinated enzyme activities concurring to the metabolism of the carcinogen(s) in question. Genetic polymorphism analysis can allow for the detection of patients more prone to some types of specific cancers, or to the adverse effects of specific pharmaceutical agents. Considering the increasingly confirmed double-edged sword nature of metabolism polymorphism (both wild-type and variant alleles can predispose to cancer, albeit in different situations of exposure), individual susceptibility to cancer should be monitored as a function of the nature, and mechanism of action, of the carcinogen(s) to which the individual under study is known to be exposed, and with reference to the main target organ of the considered type of exposure.

Lung cancer risk of the GSTM1 null genotype is enhanced in the presence of the GSTP1 mutated genotype in male Japanese smokers

The potential interaction of GSTM1 and GSTP1 genotypes in pulmonary carcinogenesis was assessed in 382 male Japanese lung cancer patients (127 squamous cell carcinoma, 78 small cell carcinoma, 177 adenocarcinoma) and 257 controls. In smokers (358 cases, 184 controls) the GSTM1 null genotype was more distributed in individuals with at least one GSTP1 mutant allele compared to those without, in lung cancer patients (69.5% vs.53.2%) but not in controls (48.0% vs. 48.5%). No such relationship was detected in non-smokers (24 cases, 73 controls). The estimated relative risk of the GSTM1 null genotype for lung cancer was 2.58 (95%CI = 1.26-5.30) in smokers with the GSTP1 mutant allele while it was 1.17 (95%CI = 0.77-1.79) in those without, suggesting that mutated GSTM1 and GSTP1 genotypes interact to potentiate the risk of lung cancers in Japanese smokers.

Polymorphisms of N-acetyltransferases, glutathione S-transferases, microsomal epoxide hydrolase and sulfotransferases: influence on cancer susceptibility

It has become clear that several polymorphisms of human drug-metabolizing enzymes influence an individual's susceptibility for chemical carcinogenesis. This review gives an overview on relevant polymorphisms of four families of drug-metabolizing enzymes. Rapid acetylators (with respect to N-acetyltransferase NAT2) were shown to have an increased risk of colon cancer, but a decreased risk of bladder cancer. In addition an association between a NAT1 variant allele (NAT*10, due to mutations in the polyadenylation site causing approximately two fold higher activity) and colorectal cancer among NAT2 rapid acetylators was observed, suggesting a possible interaction between NAT1 and NAT2. Glutathione S-transferases M1 and T1 (GSTM1 and GSTT1) are polymorphic due to large deletions in the structural gene. Meta-analysis of 12 case-control studies demonstrated a significant association between the homozygous deletion of GSTM1 (GSTM1-0) and lung cancer (odds ratio: 1.41; 95% CI: 1.23-1.61). Combination of GSTM1-0 with two allelic variants of cytochrome P4501A1 (CYP1A1), CYP1A1 m2/m2 and CYP1A1 Val/Val further increases the risk for lung cancer. Indirect mechanisms by which deletion of GSTM1 increases risk for lung cancer may include GSTM1-0 associated decreased expression of GST M3 and increased activity of CYP1A1 and 1A2. Combination of GST M1-0 and NAT2 slow acetylation was associated with markedly increased risk for lung cancer (odds ratio: 7.8; 95% CI: 1.4-78.7). In addition GSTM1-0 is clearly associated with bladder cancer and possibly also with colorectal, hepatocellular, gastric, esophageal (interaction with CYP1A1), head and neck as well as cutaneous cancer. In individuals with the GSTT1-0 genotype more chromosomal aberrations and sister chromatid exchanges (SCEs) were observed after exposure to 1,3-butadiene or various haloalkanes or haloalkenes. Evidence for an association between GSTT1-0 and myelodysplastic syndrome and acute lymphoblastic leukemia has been presented. A polymorphic site of GSTP1 (valine to isoleucine at codon 104) decreases activity to several carcinogenic diol epoxides and was associated with testicular, bladder and lung cancer. Microsomal expoxide hydrolase (mEH) is polymorphic due to amino acid variation at residues 113 and 139. Polymorphic variants of mEH were associated with hepatocellular cancer (His-113 allele), ovarian cancer (Tyr-113 allele) and chronic obstructive pulmonary disease (His-113 allele). Three human sulfotransferases (STs) are regulated by genetic polymorphisms (hDHEAST, hM-PST, TS PST). Since a large number of environmental mutagens are activated by STs an association with human cancer risk might be expected.

Effects of glutathione S-transferase (GST) M1 and GSTT1 genotypes on urothelial cancer risk

The M1 member of the mu class of the glutathione S-transferase (GSTM1) gene is present in about 50% of individuals. GSTT1, a member of the theta class, which has been recently shown to be polymorphic, is expressed in 35-90% of individuals. In this study, 145 Japanese patients with urothelial transitional cell carcinoma and 145 healthy controls, frequency-matched for age and gender, were compared for frequencies of GSTM1 and GSTT1 genotypes. The urothelial cancer risk increased due to the GSTM1 null genotype (odds ratio (OR) 1.71, 95% confidence interval (CI) 1.05-2.79). On the other hand, the OR tended to decrease due to the GSTT1 null genotype, although not significantly. Among individuals of the GSTM1 null genotype, those of the GSTT1-positive genotype had a two-fold risk (OR 2.62, 95% CI 1.36-5.05) compared with the GSTT1 null genotype (OR 1.25, 95% CI 0.62-2.51). A significant interaction between the GSTM1 genotype and smoking status was found; the GSTM1 null genotype was associated with an increased risk of urothelial cancer among smokers (OR 1.98, 95% CI 1.10-3.57).