p53 codon 72 polymorphism associated with risk of human papillomavirus-associated squamous cell carcinoma of the oropharynx in never-smokers.
ABSTRACT The tumor suppressor p53 protein can be bound, degraded and inactivated by the human papillomavirus (HPV) E6 oncoprotein. The p53 protein's susceptibility to this oncoprotein may be influenced by the p53 codon 72 polymorphism, but the role of such a polymorphism in the development of HPV16-associated squamous cell carcinoma of the oropharynx (SCCOP) has not been established. To investigate the role of the p53 codon 72 polymorphism in the risk of HPV16-associated SCCOP, we conducted a hospital-based case-control study of 188 non-Hispanic white patients with newly diagnosed SCCOP and 342 cancer-free control subjects frequency matched by age (+/-5 years), sex, tobacco smoking status and alcohol drinking status. We found that HPV16 seropositivity was associated with an increased risk of SCCOP [adjusted odds ratio (OR), 5.7; 95% confidence interval (CI), 3.7-8.7], especially among never-smokers (adjusted OR, 14.1; 95% CI, 6.0-32.9) and among subjects with the p53 codon 72 variant genotypes [Arginine (Arg)/Proline (Pro) and Pro/Pro] (adjusted OR, 9.2; 95% CI, 4.7-17.7). A significant multiplicative interaction on the risk of SCCOP was also found between the p53 codon 72 polymorphism and HPV16 seropositivity (P = 0.05). Among never-smokers, the risk of SCCOP for those who had both HPV16 seropositivity and p53 codon 72 variant genotypes (Arg/Pro + Pro/Pro) was particularly high (adjusted OR, 22.5; 95% CI, 4.8-106.2). These findings suggest that p53 codon 72 variant genotypes modify the risk of HPV16-associated SCCOP and may be markers of genetic susceptibility to HPV16-associated SCCOP, especially among never-smokers.
- Nature 12/1998; 396(6711):531-532. · 38.60 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: It has been reported that an intrinsic susceptibility to cancer is related to the way an individual responds to DNA-damaging agents. The aim of this study was to evaluate whether, in addition to bleomycin-induced chromosomal instability, radiation-induced initial DNA damage and subsequent repair is associated with the development of head-and-neck squamous-cell carcinoma. In this study, 2 assays were performed to measure DNA damage in human peripheral-blood lymphocytes. One was a chromosomal aberration assay which determines sensitivity to chromatid breaks induced by bleomycin, the other an elegant immunochemical assay which measures the level of radiation-induced strand breaks as well as subsequent repair. Age, smoking and alcohol-drinking behavior did not influence the number of chromatid breaks, initial DNA damage or repair capacity. As has been found in previous studies, the mean number of chromatid breaks per cell was significantly different between patients (n = 18) and control persons (n = 19), whereas the amount of initial DNA damage was not. No correlation was found between the outcome of the 2 assays in the subject groups. In contrast to laryngeal-carcinoma patients, oral-cavity-carcinoma patients showed significantly slower repair capacity than controls. Our hypothesis is that the way DNA damage is processed by the patients determines at which site cancer develops in the head and neck area.International Journal of Cancer 10/1996; 68(1):26-9. · 6.20 Impact Factor
Article: Control of apoptosis by p53.[show abstract] [hide abstract]
ABSTRACT: The p53 tumor suppressor acts to integrate multiple stress signals into a series of diverse antiproliferative responses. One of the most important p53 functions is its ability to activate apoptosis, and disruption of this process can promote tumor progression and chemoresistance. p53 apparently promotes apoptosis through transcription-dependent and -independent mechanisms that act in concert to ensure that the cell death program proceeds efficiently. Moreover, the apoptotic activity of p53 is tightly controlled, and is influenced by a series of quantitative and qualitative events that influence the outcome of p53 activation. Interestingly, other p53 family members can also promote apoptosis, either in parallel or in concert with p53. Although incomplete, our current understanding of p53 illustrates how apoptosis can be integrated into a larger tumor suppressor network controlled by different signals, environmental factors, and cell type. Understanding this network in more detail will provide insights into cancer and other diseases, and will identify strategies to improve their therapeutic treatment.Oncogene 01/2004; 22(56):9030-40. · 7.36 Impact Factor
Carcinogenesis vol.29 no.4 pp.875–879, 2008
Advance Access publication February 6, 2008
p53 codon 72 polymorphism associated with risk of human papillomavirus-associated
squamous cell carcinoma of the oropharynx in never-smokers
Xuemei Ji1, Ana S.Neumann2,3, Erich M.Sturgis1,2, Karen
Adler-Storthz4, Kristina R. Dahlstrom1,5, John T.Schiller6,
Qingyi Wei2and Guojun Li1,2,?
1Department of Head and Neck Surgery and2Department of Epidemiology,
The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe
Boulevard, Houston, TX 77030, USA,3Dental Division of the Royal
Children’s Hospital, Melbourne 3052, Australia,4Department of Diagnostic
Sciences, The University of Texas Health Science Center-Dental Branch,
Houston, TX 77030, USA,5Department of Genetics and Developmental
Medicine, University of Washington, Seattle, WA 98195, USA and
6Laboratory of Cellular Oncology, National Cancer Institute, National
Institutes of Health, Bethesda, MD 20892, USA
?To whom correspondence should be addressed. Tel: þ1 713 792 0227;
Fax: þ1 713 794 4662;
The tumor suppressor p53 protein can be bound, degraded and
inactivated by the human papillomavirus (HPV) E6 oncoprotein.
The p53 protein’s susceptibility to this oncoprotein may be influ-
enced by the p53 codon 72 polymorphism, but the role of such
a polymorphism in the development of HPV16-associated squa-
mous cell carcinoma of the oropharynx (SCCOP) has not been
established. To investigate the role of the p53 codon 72 polymor-
phism in the risk of HPV16-associated SCCOP, we conducted
a hospital-based case–control study of 188 non-Hispanic white
patients with newly diagnosed SCCOP and 342 cancer-free con-
trol subjects frequency matched by age (±5 years), sex, tobacco
smoking status and alcohol drinking status. We found that HPV16
seropositivity was associated with an increased risk of SCCOP
[adjusted odds ratio (OR), 5.7; 95% confidence interval (CI),
3.7–8.7], especially among never-smokers (adjusted OR, 14.1;
95% CI, 6.0–32.9) and among subjects with the p53 codon 72
variant genotypes [Arginine (Arg)/Proline (Pro) and Pro/Pro]
(adjusted OR, 9.2; 95% CI, 4.7–17.7). A significant multiplicative
interaction on the risk of SCCOP was also found between the p53
codon 72 polymorphism and HPV16 seropositivity (P 5 0.05).
Among never-smokers, the risk of SCCOP for those who had both
HPV16 seropositivity and p53 codon 72 variant genotypes (Arg/
Pro 1 Pro/Pro) was particularly high (adjusted OR, 22.5; 95%
CI, 4.8–106.2). These findings suggest that p53 codon 72 variant
genotypes modify the risk of HPV16-associated SCCOP and may
be markers of genetic susceptibility to HPV16-associated SCCOP,
especially among never-smokers.
Squamous cell carcinoma of the head and neck, which includes squa-
mous cell carcinomas of the oral cavity, oropharynx, hypopharynx
and larynx, is among the five most common cancers and accounts
for .500 000 new cases every year worldwide (1). The leading risk
factors forthese cancers are tobacco use and alcohol consumption; but
over the past decade, oncogenic human papillomavirus (HPV) has
been repeatedly detected in squamous cell carcinoma of the orophar-
ynx (SCCOP) (2). In numerous studies, ?50% (39–73%) of SCCOP
cases have been found to contain portions of the HPV genome (3–6),
suggesting that HPV plays an etiologic role in subset of SCCOP,
termed HPV-associated SCCOP. Unlike HPV-negative tumors,
HPV-associated tumors tend to have the wild-type p53 gene and
HPV DNA, express HPV E6 and/or E7, have decreased expression
of cyclin D and pRb and have upregulated p16 (7–9). Of the known
HPV types, oncogenic HPV16 is the most frequent, accounting for
?90% of HPV-associated tumors of the oropharynx (5,10,11). The
presence of HPV16 antibodies, a marker of past exposure to HPV16,
has been positively associated with increased risk of cervical cancer
(12,13) and SCCOP (11,14–17). Although HPV infection may be
a major risk factor for SCCOP (5,10), the malignant conversion of
oropharyngeal infection by oncogenic HPVis uncommon, suggesting
The p53 protein, as a tumor suppressor, has a highly conserved role
as a ‘guardian of the genome’ and is central to cellular anticancer
mechanisms (18). In response to genotoxic injuries, p53 can dictate
cellular fate (19–21) by initiating cell cycle arrest, promoting DNA
repair (22), triggering apoptosis (23) and inducing growth arrest and
senescence (24). Although direct mutations can alter or inactivate
p53, interactions with the oncogene products of oncogenic viruses
(e.g. HPV) can also cause aberrations in the p53 regulation (23,25).
The malignant transforming potential of oncogenic HPV is attributed
to its oncoproteins, E6 and E7 (26), and the E6 oncoprotein can bind
to the tumor suppressor p53, promoting ubiquitination and rapid pro-
teasome-mediated degradation (27,28). Because of the important
roles that p53 plays in carcinogenesis and the complex relationship
between p53 and HPVoncogenes, it is reasonable to expect that p53
polymorphisms can modify interindividual variations in susceptibility
to cancer. To date, 20 non-synonymous polymorphisms have been
identified in the human p53 gene (29). Among them, the polymor-
phism in codon 72 of exon 4, encoding either Proline (Pro) or Argi-
nine (Arg), has been proven to influence functional activity, mutant
behavior, susceptibility to SCCOP and response to treatment (30,31).
Compared with p53 72Pro, p53 72Arg appears to suppress cellular
transformation more effectively, to induce apoptosis more efficiently
(32), but to be possibly more susceptible to HPV E6-mediated deg-
radation (33). In addition, some studies have suggested that this poly-
morphism is correlated with the risk of HPV-associated cervical
Several studies have examined the effect of p53 codon 72 poly-
morphism on the risk of HPV-associated squamous cell carcinomas of
head and neck (35–37). However, to our knowledge, only one study
was restricted to SCCOP, finding that p53 Pro/Pro genotype was a risk
factor for HPV-associated SCCOP in a case–control study of 77
SCCOP patients and 141 controlsubjects without adjustment for other
confounders, such as smoking and alcohol consumption (36). To fur-
ther investigate the possible roles of the p53 codon 72 polymorphism
in the risk of HPV-associated SCCOP, we evaluated the relationship
between the p53 codon 72 polymorphism and HPV16 serological
status and explored the joint effects of p53 genotypes and HPV16
serological status in subgroups of subjects stratified by smoking status
in a case–control study of 188 case subjects newly diagnosed with
SCCOP and 342 cancer-free control subjects.
Materials and methods
Consecutive patients with newly diagnosed, histopathologically confirmed and
untreated SCCOP were recruited between May 1996 and January 2001 through
the Head and Neck Center at The University of Texas, M. D. Anderson Cancer
Center (MDACC) in Houston, Texas, as part of a molecular epidemiologic
study of squamous cell carcinoma of the head and neck. The controls included
two groups of cancer-free subjects. One group were 156 (45.6%) healthy
controls who were selected from a control pool of enrollees at the Kelsey-
Seybold Clinic, a multi-specialty physician practice with multiple clinics
Abbreviations: Arg, Arginine; CI, confidence interval; HPV, human papillo-
mavirus; MDACC, M. D. Anderson Cancer Center; OR, odds ratio; PCR,
polymerase chain reaction; Pro, Proline; SCCOP, squamous cell carcinoma
of the oropharynx.
? The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: firstname.lastname@example.org
by guest on June 3, 2013
throughout the Houston metropolitan area. The overall response rate was
?75%. The other controls were 186 (54.4%) healthy visitors who were accom-
panying cancer patients to the outpatient clinics at MDACC but genetically
unrelated to the cases. The response rate for this MDACC control group was
?80%. The accrual rate was 81% for the cases. Both control groups had no
previous history of any cancer and were not on therapies or treatment for any
diseases and were frequency matched to the cases on age (±5 years), gender
and smoking status. To avoid confounding due to ethnic characteristics, we
included only non-Hispanic whites in both the case and the control groups.
Participants who had smoked .100 cigarettes in their lifetimes were cate-
gorized as ‘ever-smokers’ and the rest as ‘never-smokers’. Participants who
had drunk alcoholic beverages at least once a week for .1 year were catego-
rized as ‘ever-drinkers’ and the rest as ‘never-drinkers’. ‘Former smokers’ and
‘former drinkers’ were defined as those ever-smokers and ever-drinkers who
had quit such behavior for at least 1 year before enrollment in the study and the
remaining ever-smokers and ever-drinkers were defined as ‘current smokers’
and ‘current drinkers’. After signing informed consent forms, which had been
approved by the institutional review boards of both MDACC and Kelsey-
Seybold, study participants completed a questionnaire regarding demographic
and relevant risk factors and donated 30 ml of blood.
HPV16 serological testing
HPV16 L1 virus-like particles generated from recombinant baculovirus-
of study subjects by using a standard enzyme-linked immunosorbent assay, as
described previously (12,38). Control sera, known to be positive and negative,
were also tested in parallel with the study samples in duplicate on each plate.
The cutoff level, above which optical density values were considered positive
and below which optical density values were considered negative for HPV16,
was based on the absorbance value of a standard pooled serum known to be at
the threshold of detection. Samples that were in 15% of the cutoff were tested
twice more; those positive in all three runs were considered positive. We also
randomly selected 10% of the samples to retest for confirmation of the original
findings. To eliminate potential binding interference by heparin, we treated the
plasma samples with 43 U/ml heparinase I (Sigma, St Louis, MO) before
testing (39). We tested heparinized plasma, as well as serum, obtained from
three individuals and did not detect discernible difference between the reac-
tions of the serum samples and the heparinized plasma samples treated with
Leukocyte cell pellets were obtained from the buffy coat by centrifugation of
1 ml of each subject’s whole blood; then, genomic DNA was extracted from
each pellet using the Qiagen DNA Blood Mini Kit (Qiagen, Valencia, CA)
according to the manufacturer’s instructions. We used polymerase chain re-
p53 polymorphism in codon72
The PCR reaction was performed in 25 ll volumes containing ?50 ng of
genomic DNA template, 12.5 pmol of each primer, 0.1 mM of each deoxy-
nucleoside triphosphate, 1? PCR buffer (50 mM KCl, 10 mM Tris–HCl and
0.1% Triton X-100), 1.5 mM MgCl2and 1.5 U of Taq polymerase (Promega
Corporation, Madison, WI). PCR amplification involved an initial denaturation
step at 94?C for 4 min, 35 cycles of 94?C for 40 s, 56?C for 30 s and 72?C for
30 s; and a final extension at 72?C for 10 min. Then, the PCR product (a 296 bp
fragment) was digested by BstUI (New England BioLabs, Beverly, MA) over-
night at 60?C and resolved on 2.5% NuSieve 3:1 agarose gel (FMC BioProd-
ucts, Rockland, ME) with ethidium bromide and photographed with Polaroid
film. The p53 72Pro allele, which lacked the BstUI restriction site, had only
a single 296 bp band, whereas p53 72Arg, which had the BstUI restriction site,
produced 169 and 127 bp bands. More than 10% of the samples were retested
randomly, and the results were 100% concordant.
All the statistical analyses were performed with Statistical Analysis System
software (Version 9.1; SAS Institute, Cary, NC). The differences in the distri-
butions of selected demographic variables, tobacco smoking, alcohol drinking
and p53 allele and genotype frequencies between cases and controls were
evaluated using the v2test. Both univariate and multivariate logistic regression
analyseswere usedto calculateoddsratios(ORs)and95% confidenceintervals
(CIs) for cases and controls who were stratified by age, sex, p53 genotype,
smoking, drinking and HPV16 status. In the multivariate logistic regression
model, OR and 95% CI were adjusted by age, sex, smoking and drinking.
Because only a small number of individuals (11 cases and 23 controls) were
homozygous for the Pro allele, precluding meaningful subgroup analyses, p53
genotype data were dichotomized according to a dominant model, in which
homozygosity for Arg/Arg was coded as zero and the heterozygous state and
homozygosity for Pro/Pro were coded as one. All tests were two sided, and
a P value of 0.05 was considered as the cutoff for statistical significance.
The distributions of demographic variables and risk factors of the 188
cases and the 342 cancer-free controls are summarized in Table I. All
were non-Hispanic whites and the two groups appeared to be ade-
quately frequency matched for age, sex, smoking and alcohol con-
sumption, but these factors were also adjusted for in later analyses for
controlling any residual effects. When comparing p53 codon 72 ge-
notype distributions between cases and controls, no significant differ-
ences were found (v25 0.356, P 5 0.837). The distributions of
p53 genotypes among the controls were in agreement with Hardy–
Weinberg equilibrium (v25 0.391, P 5 0.532). The p53 codon
72Pro allele was present in 45.2% of the cases and 47.6% of the
cancer-free controls (P 5 0.661), and the p53 codon 72Pro allele
frequency was 25.5% in the cases and 27.2% in the controls
(P 5 0.598). We also found that the distribution of p53 72Pro carriers
and non-carriers was similar between the cases and controls, and this
difference was not statistically significant (v25 0.292, P 5 0.589).
However, the HPV16 seropositivity was significantly more common
in cases than in controls (P , 0.001).
As shown in Table II, HPV16 seropositivity was associated with
a .5-fold risk of SCCOP (OR, 5.7; 95% CI, 3.7–8.7) after adjusting
for age, sex, smoking status and drinking status. While HPV16 sero-
positivity among those with the p53 homozygous wild-type (Arg/Arg)
genotype was associated with an elevated risk of SCCOP (OR, 3.9;
95% CI, 2.2–7.0), among individuals with the p53 Arg/Pro and Pro/
Pro genotypes, HPV16 seropositivity was associated with an even
greater risk of SCCOP (adjusted OR, 9.2; 95% CI, 4.7–17.7). Al-
though the 95% CIs of these risk estimates overlap one another, we
did find a significant interaction between HPV16 serologic status
(seropositive versus seronegative) and p53 codon 72 polymorphism
Table I. Frequency distribution of demographic and risk factors in SCCOP
cases and controls
VariablesCases (no. 5 188) Controls (no. 5 342)P valuea
bv25 0.356, P 5 0.837 for genotype distributions; v25 0.278, P 5 0.598
for allele frequency; the observed genotype frequencies among the controls
were in agreement with Hardy–Weinberg equilibrium (p2þ 2pq þ q25 1)
(v250.391, P 5 0.532).
X.Ji et al.
by guest on June 3, 2013
(p53 72Pro carriers versus non-carriers) on the risk of SCCOP, but the
interaction is only marginally significant (P 5 0.05).
To identify other factors affecting risk of HPV16-associated
SCCOP, we further stratified the associations between the HPV16
status and the cancer risk by age, sex, smoking and alcohol drinking.
We found that risk of SCCOP associated with HPV16 seropositivity
was evident for all the subgroups, but particularly more pronounced
among men (OR, 6.1; 95% CI, 3.8–9.8), individuals ,56 years old
(OR, 7.3; 95% CI, 3.9–13.4), never-smokers (OR, 14.1; 95% CI,
6.0–32.9) and never-drinkers (OR, 10.9; 95% CI, 4.0–29.5). However,
the interaction between HPV16 status and sex, age and alcohol drink-
ing was not statistically significant (P 5 0.442 for sex, P 5 0.182 for
age and P 5 0.177 for alcohol drinking, respectively). We did find
a significant interaction between HPV16 status and smoking status
(P 5 0.015) (Table II).
We also found a significant three-way interaction between HPV16
serologic status, p53 codon 72 genotype and smoking status (P 5
0.006), and therefore we stratified the risk by HPV16 serological
status, p53 genotype and smoking status, with adjustment for age,
sex and drinking status (Table III). Those never-smokers who were
HPV16 seropositive and had variant p53 genotypes exhibited
a .22-fold greater risk of SCCOP (adjusted OR, 22.5; 95% CI,
4.8–106.2) than those never-smokers who were HPV16-negative
and had the wild-type genotype, but this result could be caused by
chance due to the small sample sizes in each subgroups. We need
further studies with larger sample sizes to confirm this finding. How-
ever, HPV16 seropositivity in never-smokers with the Arg/Arg geno-
type conferred only a 5-fold risk of SCCOP (adjusted OR, 4.9; 95%
CI, 1.8–13.2). Ever-smokers who had variant p53 genotypes and were
HPV16 seropositive exhibited a 4.2-fold greater risk of SCCOP (ad-
justed OR, 4.2; 95% CI, 2.0–8.6) than ever-smokers who had thewild-
type genotype and were HPV16 seronegative. Ever-smokers with the
wild-type genotype who were HPV16 seropositive exhibited a similar
but slightly less increased risk of SCCOP (adjusted OR, 3.4; 95% CI,
1.7–6.8). In this stratified analysis, we also found that, compared with
the p53 Arg/Arg genotype, the variant p53 genotypes (Arg/Pro þ Pro/
Pro) were protective for never-smokers without evidence of HPV16
exposure (adjusted OR, 0.3; 95% CI, 0.1–0.8), but not for similar
ever-smokers (adjusted OR, 0.9; 95% CI, 0.5–1.6).
In this study, we found that the increase in risk of SCCOP associated
with HPV16 seropositivity was significantly greater for individuals
with p53 codon 72 variant genotypes (Arg/Pro and Pro/Pro) than for
those with the p53 Arg/Arg genotype. This finding suggests that p53
variant genotypes are risk genotypes for HPV16-associated SCCOP
and that the p53 codon 72 polymorphism may be a marker for genetic
susceptibility to HPV16-associated SCCOP. A possible explanation is
that the change from Arg to Pro alters the p53 protein, affecting p53’s
susceptibility to E6-mediated degradation, apoptosis potency and
transcriptional activity (32), thereby increasing the carcinogenic po-
tential of HPV16.
Storey et al. (33) were the first to suggest that individuals homo-
zygous for p53 72Arg have a 7-fold greater risk of HPV-associated
cancers than the heterozygotes. Since then, several studies have ex-
amined the associations between the p53 codon 72 polymorphism,
HPVinfection and head and neck cancer risk, with inconsistent results
(35–37,40). For example, Katiyar et al. (35) found no association
between the p53 codon 72 polymorphism and the risk of HPV-asso-
ciated oral cancer in 13 patients with HPV-positive carcinomas, 31
patients with HPV-negative carcinomas and 20 healthy controls from
an Indian population. Another study of 202 patients with oral cancer
and 333 healthy controls also found no association between the p53
codon 72 polymorphism and HPV status or between the p53 codon 72
polymorphism and risk of oral cancer (37). Recently, another study,
Table II. Adjusted ORs and 95% CIs of selected variables and risk of HPV16-associated SCCOP
VariablesHPV16 status CasesControlsP values for interactiona
No.% No.% Adjusted OR (95% CI)b
P53 Arg/Pro þ Pro/Pro
aInteraction between HPV16 status (seropositive versus seronegative) and p53 polymorphism (72Pro carriers versus non-carriers), age, sex, smoking and alcohol
bHPV positive versus HPV negative in each stratum; ORs were adjusted for age, sex, smoking and alcohol drinking accordingly in logistic regression models.
p53 polymorphisms and HPV-associated squamous cell carcinoma of the oropharynx in never-smokers
by guest on June 3, 2013
which investigated squamous cell carcinomas of the head and neck in
122 patients (44 with laryngeal cancer, 33 with oropharyngeal cancer,
30 with hypopharyngeal cancer, 13 with oral cavity cancer, one with
cancer of the ear and one with cancer of the nose) and 193 healthy
individuals also found no significant association between the p53
polymorphism and HPVexpression level (40).
However, when Perrone et al. (36) explored the association of the
p53 codon 72 polymorphism with HPV-associated SCCOP in 77 cases
and 141 cancer-free controls, they found that the p53 Pro/Pro geno-
type was a risk factor for developing HPV16-associated SCCOP,
which is consistent with the results reported here. However, unlike
the current study, those results evaluated the risk of SCCOP without
adjusting or segregating data for smoking or drinking status. More-
over, several studies found that individuals with the p53 72Pro allele
were at higher risk of developing cervical cancers, nearly all of which
were HPV-positive, than those with the p53 72Arg allele (20,41,42).
The contradictory results from all these studies may be due to the
differences in tumor sites, sample sizes and ethnic groups studied. In
fact, yet other previous studies have suggested that environmental risk
factors, such as HPV infection, and genetic predispositions, such as
the p53 codon 72 polymorphism, may contribute differently to cancer
risk depending on the specific anatomic site, even within the head and
neck region (40,43,44). For example, compared with squamous cell
carcinomas at other head and neck sites, SCCOP is more likely to be
associated with HPV (4,5,8) and is therefore more likely to be asso-
ciated with the p53 codon 72 polymorphism (40). In contrast, cancers
of the oral cavity, which are rarely HPV positive, may unlikely to be
associated with p53 status, a fact that may have led to negative results
of some studies that had mixed oral cavity and SCCOP cases.
Another important finding in our study is that, among never-
smokers, p53 variant Pro genotypes were associated with a 22-fold
greater risk for the development of HPV16-associated SCCOP,
whereasamong ever-smokers,thep53 variantgenotypewasassociated
with onlya 4-fold increase in the risk of developingHPV16-associated
SCCOP. This finding implies that the p53 codon 72 polymorphism
may have an increased interaction with HPV16 among never-smokers
and that smoking and p53 variants may not be cofactors in the etiol-
ogy of HPV16-associated SCCOP, possibly because tobacco use and
HPVinfection, the two major etiologic agents for SCCOP, both target
p53 and disrupt the p53 pathway through different mechanisms. In
other words, the p53 codon 72 polymorphism may be important to
carcinogenesis of HPV16-associated oropharyngeal cancers, but not
other oropharyngeal cancers. To our knowledge, no studies have in-
vestigated the associations between the p53 codon 72 polymorphism
and HPV-associated cancers according to the patient’s smoking status.
Although this study strongly provides evidence of interplay between
the p53 codon 72 polymorphism, smoking status and HPV16-associ-
ated SCCOP,these findings need tobevalidated infurther studieswith
Despite these intriguing results in this relatively large group of
subjects compared with previously published reports, our study also
has some limitations. For instance, because this was a hospital-based
case–control study, there may have been some selection bias in that
our cases and controls were from different populations: SCCOP cases
were enrolled from the MDACC patients, and controls were recruited
from outpatient clinics visitors at MDACC and a control pool of
enrollees at the Kelsey-Seybold Clinic through the Houston metro-
politan area. However, as others have also found (45–48), the differ-
ence in the frequency of p53 genotypes between cases and controls
was not statistically significant. Also, as in other studies, our findings
confirmed that HPV16 infection is a risk factor for SCCOP and that
the risk associated with HPV16 seropositivity is higher among men,
younger individuals (46), never-drinkers (49) and never-smokers
(4,5,11,38). In addition, because our study included only non-
Hispanic white subjects, and the cases and controls were frequency
matched for age, sex, smoking status and drinking status, the effects
of any confounding demographic factors might have been minimized.
Another limitation may be that the stratified analyses had a limited
number of individuals in each category, so our results should be
confirmed in larger studies. Furthermore, HPV16 seropositivity might
not reflect actual tumor molecular events, and some patients may be
classified as serologically negative when their tumors were actually
HPV16 DNA positive. However, Herrero et al. (11) have shown a rea-
sonable concordance between HPV16 seropositivity and SCCOP tu-
mor HPV16 DNA positivity; furthermore, using serologic status
allows for the inclusion of a cancer-free control group.
In summary, our study provides evidence that p53 codon 72 variant
genotypes are risk factors for HPV16-associated SCCOP in a non-
Hispanic white population. We also found that p53 codon 72 variant
genotypes were associated with a strikingly higher risk for HPV16-
associated SCCOP in never-smokers than in smokers. To our knowl-
edge, this is the largest study to investigate the association between
the p53 codon 72 polymorphism and HPV16-associated SCCOP with
stratification by smoking status. To advance these findings, we are
currently testing other functional polymorphisms of members of the
p53 family to elucidate the roles of these genetic variants in the
pathology of HPV-positive and HPV-negative SCCOP, and we en-
courage future studies of these genotypes and their interaction with
HPVand smoking in molecular epidemiologic studies restricted to the
The University of Texas MDACC to E.M.S.; the National Institutes of
Health Head and Neck SPORE Career Development Award
(P50CA097007) to E.M.S.; the University of Texas MDACC Institu-
tional Research to E.M.S.; the National Institutes of Health (ES
Table III. Stratification of risk of SCCOP in never- and ever-smokers by p53 genotype and HPV16 exposure
Smoking status and p53 genotype HPV16 statusCases ControlsCrude OR (95% CI) AdjustedaOR (95% CI)
Arg/Pro þ Pro/Pro
Arg/Pro þ Pro/Pro
Arg/Pro þ Pro/Pro
Arg/Pro þ Pro/Pro
4.2 (2.0–8.6) 20.8
aAdjusted for age, sex and alcohol in logistic regression models.
X.Ji et al.
by guest on June 3, 2013
11740) to Q.W.; the Clinician Investigator Award (K-12 CA88084) to
E.M.S.; and the National Institutes of Health Cancer Center Support,
MDACC (CA 16672).
The authors thank Angelique Siy for manuscript editing; Margaret Lung,
Liliana Mugartegui and Angeli Fairly for their help with subject recruitment
and Li-E Wang for laboratory management.
Conflict of Interest Statement: None declared.
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Received October 22, 2007; revised January 10, 2008;
accepted January 29, 2008
p53 polymorphisms and HPV-associated squamous cell carcinoma of the oropharynx in never-smokers
by guest on June 3, 2013