Grantee Research Project Results
Final Report: Genetic Polymorphisms and Interindividual Variation in Susceptability to Cancer of the Oropharynx
EPA Grant Number: R825282Title: Genetic Polymorphisms and Interindividual Variation in Susceptability to Cancer of the Oropharynx
Investigators: Henner, William D.
Institution: Oregon Health & Sciences University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1996 through September 30, 1999 (Extended to September 30, 2000)
Project Amount: $616,325
RFA: Role of Interindividual Variation in Human Susceptibility to Cancer (1996) RFA Text | Recipients Lists
Research Category: Human Health
Objective:
The overall purpose of the study was to identify the role of human genetic polymorphisms in the susceptibility of individuals to environmentally induced cancers. Polymorphisms in both detoxification enzymes and oncogenes were studied. The model studied was human squamous cell cancer of the oropharynx and the type of study was a case control. We enrolled cases with squamous cell cancer (SCC) oropharynx and appropriately matched controls. Genetic polymorphisms were determined by PCR-based technology.Summary/Accomplishments (Outputs/Outcomes):
During the period of the report, this project completed enrollment of head and neck squamous cell cancer (HNSCC) case and control subjects. A total of 359 cases and 399 control subjects were enrolled and blood samples obtained for DNA preparation.Characteristics of Malignancies. For each case of HNSCC, the original histology report was obtained and the diagnosis confirmed. The location of the primary tumor for each of the cases confirmed is as follows:
Location
|
Count
|
Percent
|
Lip and Oral Cavity | 128 | 36 |
Pharynx | 81 | 23 |
Larynx | 119 | 33 |
Paranasal Sinus | 22 | 6 |
HNSCC NOS | 7 | 2 |
Total | 357 | 100 |
The size of the primary tumor in these cases was:
Tumor Size
|
Percent
|
T1 | 16 |
T2 | 25 |
T3 | 25 |
T4 | 39 |
Whether or not the regional lymph nodes were involved at the time of initial surgery also was determined from the pathology report. Regional nodes were positive for metastatic malignancy in 26 percent of cases. Only three cases (1.5 percent) had evidence for distant metastases at the time of their original surgery. The majority of the cases (64 percent) were incident (defined as diagnosed within two years of study enrollment) while only 36 percent had been diagnosed more than 2 years prior to enrollment.
The demographics of the patient population both cases and controls are as follows:
Controls
|
Cases
|
|
Age (years)
|
||
Mean (SD)
|
52 (12)
|
62 (13)
|
Median
|
50
|
63
|
Gender
|
||
Male
|
47%
|
68%
|
Female
|
53%
|
32%
|
Race
|
||
Caucasian
|
82%
|
96%
|
Non-Caucasian
|
12%
|
4%
|
Unknown
|
8%
|
0%
|
The racial distribution of cases and controls is essentially that of the study catchment area in the Portland Metropolitan area. The number of non-Caucasians (predominantly Black and Asian) in the study was too small to allow any conclusions to be drawn for any non-Caucasian subgroup. The median and mean age of cases is significantly older than that of controls consistent with age as a known risk factor for the development of HNSCC.
Each of the cases and controls in the study completed a questionnaire regarding cancer history, family history of cancer and exposure to tobacco products and ethanol. The Smoking and Alcohol Use reported was as follows:
Controls | Cases | |
Smoking Pack Years | ||
Mean (SD) | 26 (27) | 47 (36) |
Median | 20 | 45 |
Ever vs. Never Smoking | ||
Never Smoker | 24% | 13% |
Ever-Smoker | 76% | 87% |
Alcohol Use Ounce Years | ||
Mean | 24 | 57 |
Median | 6 | 35 |
Although the cases show a markedly increased history of tobacco exposure with approximately twice the average pack years as controls, this underestimates the effect of smoking as a risk factor in this population. In order to isolate the effect of genetic polymorphisms as a risk for HNSCC, the control population was purposely recruited from a population of smokers. Thus, smokers are over-represented in the control subjects as compared to the overall population of those without HNSCC. The cases also used alcohol substantially more than the control group.
Analysis of Genetic Polymorphisms. Five genetic polymorphisms common to the population in this study were selected for analysis. These included three glutathione transferase genes that encode detoxification enzymes, GSTM1, GSTT1 and GSTP1, a cytochrome p450, the tumor suppressor p53 and a gene encoding a DNA repair enzyme HOGG. The polymorphisms studied included GSTM1 and GSTT1 gene deletions, the GSTP1A polymorphism, the common CYP1A1 polymorphism, the codon 7 polymorphism of HOGG and the codon 72 polymorphism of p53. In each case DNA was prepared from the peripheral blood of subjects and subjected to PCR using appropriate paired primers for the region of the gene of interest. In the case of the GSTM1 and GSTT1 deletion genotypes, the absence of an appropriately sized PCR product on agarose gel electrophoresis indicated the homozygous deletion of the gene as is well established. In the case of the GSTP1A, HOGG7 and p53(codon72) polymorphisms, the single nucleotide polymorphisms (SNPs) produced a Restriction Fragment Length Polymorphism (RFLP). The presence or absence of the RFLP was assessed by gel electrophoresis following digestion of the PCR products with the appropriate restriction enzyme. This allows assessment of all three genotypes wt/wt, wt/mut and mut/mut for each SNP.
Odds Ratios. Chi Square Analysis. The results of the genotyping for each case and control were recorded and the data analyzed using the Chi-Square test. The results are as follows:
Gene/SNP | Odds Ratio | 95% CI | P value |
GSTM1 | .98 | .69-1.39 | .98 |
GSTP1 |
.81 | .45-1.49 | .44 |
GSTT1 | .60 | .39-.91 | .02 |
CYP1A1 | .66 | .13-3.3 | .93 |
P53 | .71 | .36-1.42 | .43 |
HOGG | .60 | .27-1.35 | .30 |
Based on these results, it appears that of the polymorphisms tested, only the homozygous deletion of the GSTT1 appears to be significantly associated with an altered risk of HNSCC. In the case of GSTT1, it is the subjects that bear the homozygous deletion (~30 percent of control population) who have the lowest risk of developing HNSCC. This makes biological and biochemical sense as the GSTT1 enzyme is known to be capable of activating a number of carcinogens to an alkylating moiety. The protective effect of GSTT1 deletion was most marked in women (OR .33, p <.005) and heavy ( > 45 pack years) smokers (OR .41. p < .01).
Logistic Regression. The effect of SNP genotype on risk of HNSCC also was examined by logistic regression. In logistic regression, the initial model included the known risk factors for HNSCC including age, gender, smoking and alcohol use. Each of the polymorphisms was then added singly and in pairs to the regression. Again, the only polymorphism that was associated with an altered risk of HNSCC was the GSTT1 deletion. In the logistic regression model, GSTT1 deletion was again associated with a significant ( p =.02) protective effect (OR .59). When only incident cases were examined the effect was unchanged.
In summary, squamous cell carcinoma of the head and neck is clearly a disease
strongly associated with chronic heavy exposure to tobacco and alcohol. Our
study revealed no significant increase in a family history of HNSCC in the
subjects as compared to controls. In addition, several of the common genetic
polymorphisms that have been linked to altered risk of smoking related cancers
at other sites such as lung, esophagus and bladder were not associated with
the risk of HNSCC whether or not the data were adjusted for smoking and alcohol
exposure. The observed association of GSTT1 deletion with a reduced risk of
HNSCC may be useful in identifying a portion of the population at lower risk
for smoking related cancers at this and other sites. Further studies using
the DNA samples obtained in this study are planned to examine other genetic
polymorphisms as risk factors for HNSCC.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 1 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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McWilliams JE, Evans AJ, Beer TM, Andersen PE, Cohen JI, Everts EC, Henner WD. Genetic polymorphisms in head and neck cancer risk. Head Neck 2000;22(6):609-617. |
R825282 (Final) |
not available |
Supplemental Keywords:
carcinogen, genetic predisposition, ethnic groups, susceptibility, epidemiology, Pacific Northwest., RFA, Health, Scientific Discipline, Waste, Genetics, Risk Assessments, chemical mixtures, cancer risk, risk factors, interindividual variations, p53 genes, ethnic groups, lung cancer, oropharynx, carcinogens, genetic polymorphisms, human exposure, cancer risk assessment, oncogenesProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.