Research Article
Functional Polymorphisms in the Cyclooxygenase 2 (COX-2) Gene And Risk of Breast Cancer in North Indian Population
Satya N Das1*, Rekha Kataria1 and Rajinder Parshad2
*Corresponding author: Satya N Das, Departments of Biotechnology, All India Institute of Medical Sciences, India
Published: 10 Oct, 2017
Cite this article as: Das SN, Kataria R, Parshad R.
Functional Polymorphisms in the
Cyclooxygenase 2 (COX-2) Gene And
Risk of Breast Cancer in North Indian
Population. Clin Oncol. 2017; 2: 1360.
Abstract
Introduction: COX-2 is a rate limiting enzyme involved in carcinogenesis, immunosuppression,
inhibition of apoptosis, angiogenesis, tumor cell invasion and metastasis. Enhanced expression
of COX-2 has been observed in several forms of cancer such as gastric cancer, breast cancer
and esophageal cancer. Single nucleotide polymorphisms (SNPs) in the COX-2 promoter
might contribute to differential COX-2 expression and subsequent interindividual variation in
susceptibility to cancer. Hence, we assessed the association of COX-2 promoter Single Nucleotide
Polymorphisms (SNPs) (-1195G/A, -765G/C and 8473C/T) with breast cancer.
Materials and Method: Genotyping was performed in 82 biopsy proven patients and 49 (34 in case
of -765) age and sex-matched healthy control subjects by polymerase chain reaction - restriction
fragment length polymorphism (PCR-RFLP) analysis.
Result: Logistic regression analyses revealed that no overall significant associations were detected
in the single-locus analysis between the -765, -1195 and 8473 polymorphisms of COX-2 and the
risk of breast cancer. However, a significantly increased risk was associated with the combined
genotypes containing more than 3 variant alleles (OR= 2.05, 95% CI = 0.816-5.17) compared with
the combined genotypes with 0-3 variant alleles. Haplotype frequency analysis suggest that A-1195G-
765T8473 was more prevalent in patients when compared with the normals whereas G-1195C-765C8473,
A-1195C-765C8473 and G-1195G-765C8473 were more in normals as compared to patients though the results
were not statistically significant. It appears that A-1195G-765T8473 may be related to susceptibility while
G-1195C-765C8473, A-1195C-765C8473 and G-1195G-765C8473 may be related to protection in breast cancer.
Conclusion: These findings indicate that these three variants in the regulatory regions of COX-2
may contribute to the etiology of breast cancer.
Keywords: COX-2; SNP; Breast cancer; North Indian
Introduction
The cyclooxygenase (COX) enzymes, also referred to as prostaglandin end peroxide synthase,
catalyze a key step in the conversion of arachidonate to PGH2, the immediate substrate for a series
of cell specific prostaglandin and thromboxane synthases. Prostaglandins play critical roles in
numerous biologic processes including the regulation of immune function, kidney development,
reproductive biology and gastrointestinal integrity. There are two COX isoforms: The constitutive
form, COX-1, is present in many tissues and involved in PG synthesis; and the inducible form, COX-
2, is absent from most normal tissues, and rapidly induced by growth factors, cytokines, and various
carcinogens [1,2]. COX-2 over expression was shown to increase proliferation, inhibit apoptosis,
and enhance the invasiveness of cancer cells resulting in angiogenesis [3-7]. The over expression of
COX-2 is found in many tumor types [8-12], including breast cancer [13,14]. Reported that COX-2
over expression was also associated with indicators of breast cancer development, such as lymphnode
metastasis, poor differentiation and large tumor size
Transcription regulation is the major mechanism to regulate the expression and stability of
COX-2 [15]. The 5' flanking region of the human COX-2 gene, principally involved in regulating gene
transcription, contains a canonical TATA box and several putative transcription-factor binding sites,
including cAMP-responsive element, nuclear factor-κβ, nuclear factor-IL-6, glucocorticoid response
element, polyomavirus enhancer activator 3, activator protein-2,
CAAT box/enhancer binding protein, stimulatory protein-1 (Sp1),
and a transforming growth factor-β response element suggesting
that a complex array of factors is involved in its regulation [16-18].
Found that −1195G/A polymorphism created a c-MYB binding
site and induced the higher transcriptional activity of the COX-2.
Previous studies suggested that −765G/C polymorphism in 5′UTR,
a potentially functional variant, may eliminate an Sp1-binding site
but create an E2F binding site, which results in reduced or increased
COX-2 expression [19,20]. Furthermore, some studies showed that
the 3′UTR of the murine gene for COX-2 contains several regulatory
elements altering mRNA stability and translation efficiency [21],
which play an important role in degradation, stabilization, and
translation of the transcripts. Therefore, polymorphisms in 3′UTR
of COX-2 may modify the binding affinity of regulatory factors and
alter expression of COX-2, and subsequently influence susceptibility
to cancers, including breast cancer [22-24].
The present work is motivated by the possibility that genetic
variation in the COX-2 gene could alter enzyme expression levels
or biochemical function and consequently have an impact on
prostaglandin biosynthesis. Therefore, polymorphisms might modify
the individual risk of inflammatory disease, tumor incidence, or
tumor malignancy. A second possibility is that COX-2 polymorphisms
could change the response to NSAIDs resulting in decreased or
increased sensitivity to selective or nonselective COX inhibitors.
We hypothesized that potential genetic polymorphisms in COX-2
that result in altered expression and/or activity of the protein may
modulate the inflammatory response, modifying overall breast cancer
risk or risk for subtypes of breast cancer.
Table 1
Materials and Methods
Study subjects
This study included 82 breast cancer patients and 49 cancer-free
controls. Patients were recruited from the Breast cancer clinic, All India
Institute of Medical Sciences, New Delhi, India. All cancer subjects
were histopathologically diagnosed with breast cancer. Exclusion
Criteria for normal subjects included persons with malignancies,
recent operations, trauma, infection and with genetic abnormality
infections. Exclusion criteria for patients included persons with
other associated malignancies, radiation therapy, any other chronic
diseases, malnutrition, pregnancy and child birth. After informed
consent was obtained, each subject was personally interviewed by
using a structured questionnaire to obtain study related information.
The clinicopathological characteristics of the patients are tabulated in
Table 1. After the interview, a 5-ml venous blood sample was collected
from each subject. The study was approved by the Ethical committee.
Genotyping
Genomic DNA was extracted from the peripheral blood
leukocytes pellet by standard procedures using Sodium perchlorate
method. The genotyping assays for three SNPs of COX-2 (−1195G/A,
−765G/C, and 8473C/T) were described previously [25,26] Briefly, the
PCR primer pairs were: −1195G/A F, 5′-ccctgagcactacccatgat- 3′, R,
5′-gcccttcataggagatactgg-3′; −765G/C F, 5′ tattatgaggagaatttacctttcgc-
3′, R, 5′-gctaagttgctttcaacagaagaaat-3′; and 8473C/T F,
5′-gtttgaaattttaaagtacttttgat-3′, R, 5′-tttcaaattattgtttcattgc- 3′. The 20-
μl polymerase chain reaction (PCR) mixture contained approximately
50 ng DNA (100ng DNA for -765), 12.5 pmol of each primer, 0.1 mM
of each dNTP, 10 X MgCl2 free PCR buffer and 2 U Taq polymerase.
The concentration of MgCl2 was 1.5 mM for 8473C/T and 1 mM for
−1195G/A and 2 mM for -765G/C. The PCR profile consisted of an
initial melting step of 95°C for 5 min, followed by 40 cycles of 95°C for
30 s, 61°C (for −1195 G/A) or 54°C (for −765 G/C) or 48°C (for 8473
C/T) for 40 s and 72°C for 45 s, and a final extension step of 72°C for
10 min. Restriction enzymes PvuII, HhaI and BclI (MBI fermentas)
was used to distinguish the −1195G/A, −765G/C, and 8473C/T
genotypes, respectively.
Finally, in total, 82 cancer cases and 49 controls (34 controls in
case of -765) were successfully genotyped for all three polymorphisms
of COX-2.
Stastical analysis
Statistical analysis was performed by using statistical program
GraphPad Software. The differences in the frequencies of various
alleles and genotypes between breast cancer patients and healthy
controls were performed by chi-square test (χ2 test). The P-values
obtained were further corrected (Pc) by multiplying with the number
of alleles tested. The Pc value <0.05 was considered as significant. The
odds ratio and confidence interval was calculated by the following
website:
Results
The genotype distributions and allele frequencies of COX-2
−1195G/A, −765 G/C, and 8473C/T in the cancer cases and controls
are shown in Table 2. In this study, a significant difference (Pc = 0.018)
was found in COX-2 -1195 GA genotype, where GA heterozygous
was more frequent in normals than in cancer patients suggesting a
protective role of this genotype against breast cancer. COX-2 -1195
AA and COX-2 -1195 GG were more in patients as compared to
normals though Pc value was not significant. At COX-2 -765 site,
the GG genotype was slightly more while GC was less in patients as
compared to normals (76.8% vs 67.7% and 19.5% vs 29.4%; Pc>0.05
respectively). There was no difference in the COX-2 8473CT and TT
genotype frequencies in breast cancer patients when compared to
normals. Though, the frequency of these genotypes was higher than
COX-2 8473CC genotype.
When analyzed for association of COX-2 genotypes with risk
of breast cancer incidence using unconditional logistic regression
analysis, COX-2 -1195GA and AA genotypes did not show association
(OR = 0.14, 95% CI = 0.014 to 1.31 and OR = 0.44, 95% CI = 0.049
to 3.95 respectively) with risk of breast cancer when compared with
the GG genotype taken as referent. COX-2 -765CC and GC showed
no significant association (OR = 1.09, 95% CI = 0.11 to 11.07 and OR
= 0.58, 95% CI = 0.23 to1.47 respectively) with breast cancer when
compared to the referent -765GG genotype. Results of the present
study suggest COX-2 8473 CT and CC genotype not to be significantly
associated (OR = 0.96, 95% CI= 0.47-1.99 and OR=1.65, 95% CI =
0.098-22.9 respectively) with risk of breast cancer when compared
with the TT genotype taken as referent (Table 2).
The combined effect of these three variants on breast cancer was
significantly increased in the presence of “more than 3 variant alleles”
compared with the combined genotypes with “0-3 variant alleles”
(Table 3).
Haplotype analysis was also performed and eight haplotypes
were derived from the observed genotypes of these three COX-
2 polymorphisms. Haplotype frequency analysis suggested that
A-1195G-765T8473 was more prevalent in patients when compared with
the controls whereas G-1195C-765C8473, A-1195C-765C8473 and G-1195G-765C8473
were more in controls as compared to patients though the results were
not statistically significant. We may suggest that A-1195G-765T8473 may
be related to susceptibility while G-1195C-765C8473, A-1195C-765C8473 and
G-1195G-765C8473 may be related to protectiveness against breast cancer
(Table 4).
Genotypes A-1195G-765C8473, A-1195C-765T8473 and G-1195C-765T8473 were
found to be approximately equal in both patients and controls. Thus,
it may be suggested that these may not be contributing factors for
breast cancer development in North Indian population (Table 4).
In addition, the associations of three polymorphisms of COX-2
with breast cancer risk stratified by age, menopausal status and stage
of cancer were analyzed but no significant associations found (Table
5).
Table 2
Discussion
Increased concentrations of PGE2, a major product of COX-
2, have been reported in human breast cancer and in experimental
murine mammary tumour models [25,26]. Mammary tumorigenesis
can be suppressed by both genetic and pharmacologic ablation of
COX-2, thus clearly identifying a role for COX-2 in breast neoplasia.
The expression and stability of COX-2 is subjected to complex
mechanisms regulated by various elements in both the 5′UTR and
3′UTR of the transcript. Therefore, polymorphisms in the promoter
region and 3′UTR of the COX-2 gene may potentially influence
gene expression and then modulate the individual’s susceptibility to
cancers. To investigate the impact of functional SNPs of COX-2 on
tumor development, molecular epidemiological studies have been
conducted for several cancer types, including esophageal, lung, colon
and breast [28-31].
Because of the role that COX-2 plays in breast cancer development
and progression and their aberrant expression in various types of
cancer, we hypothesized that these polymorphisms in COX-2 may
be associated with an increased risk of breast cancer attributable to
the abnormal expression of this gene. In this study, we recruited 82
breast cancer patients and 49 age, sex and ethnicity matched healthy
control subjects and genotyped COX-2 for three polymorphic sites
to test the above hypothesis. In this study, a significant difference
(Pc = 0.018) was found in COX-2 -1195 GA genotype, where GA
heterozygous was more frequent in normals than in cancer patients
suggesting a protective role of this genotype against breast cancer
[32]. Conducted a case-control study of 1026 esophageal cancer
cases and 1270 controls in a population of north China and found
that COX-2 -1195AA and −765GC genotypes were associated with
a significantly 1.72- fold (95% CI 1.35-2.20) and 2.24-fold (95% CI
1.59-3.16) increased risk of developing esophageal cancer compare
with their wild-type genotypes. However, a nested case-control
study in a Caucasian population showed that the −1195G/A
polymorphism (assigned as −798A/G) in the promoter of COX-2 was
not significantly associated with risk of advanced colorectal adenomas
[33]. For the -765G/C polymorphism [34], reported that -765C allele
was associated with an increased risk of prostate cancer in African
Americans (assigned as −899G/C) [35]. showed an elevated risk of
colon cancer in a Singapore Chinese population.
There was no change in prostate cancer in Bini Nigerians [36] and
in non-small-cell lung cancer in a Norwegian population (assigned
as 926G/C) [37]. For the molecular epidemiological studies on the
associations between COX-2 8473C/T polymorphism and cancer
susceptibility, the results were also conflicting [38,39].
In the present study, no overall significant associations were
found between the -1195G/A, -765G/C and 8473 polymorphisms and
risk of breast cancer in the single-locus analyses in this population.
Analysis of the predicted mRNA secondary structure indicated
that the 8473T>C exchange interrupts a 25 bp stem and creates an
additional loop. This suggests a potential effect on the mRNA stability
and expression, but the results of this in silico analysis remain to be
proven by in vitro data. Thus, further in vitro analyses of the genetic
regulation of COX-2 expression will be necessary before a conclusion
on the functionality of the PTGS2 8473 polymorphism can be drawn.
The combined genotypes containing “more than 3 variant alleles”
were associated with a significantly increased risk of breast cancer
(OR= 2.05, 95% CI = 0.816-5.17), suggesting that polymorphisms in
the regulatory regions of COX-2 may conjointly play a role in the
development of breast cancer as reported in a study conducted.
The frequencies of genetic polymorphisms often vary between
ethnic groups. In this study, the −1195G/A genotype frequencies were
6.1% for GG, 15.8% for GA, and 78.1% for AA which differed greatly
from those reported in Chinese population (23.3% for GG, 50.9% for
GA, and 25.8% for AA) and those reported in a Caucasian population
(3.5% for GG, 30.8% for GA, and 65.7% for AA, respectively).
Similarly, the frequencies of −765G/C genotypes in the present study
were 76.8% for GG, 19.5% for GC, 3.7% for CC which differed greatly
from those reported in Chinese population (90.5% for GG, 9.2%
for GC, 0.3% for CC) and in a U.S. Caucasian population (69.4%
for GG, 27.2% for GC, 3.4% for CC). For 8473 C/T polymorphism,
the frequencies of 8473C/T in the present study were 40.2% for TT,
58.5% for CT, 1.3% for CC which differed from those in Chinese
population (67.2% for TT, 29.8% for CT, 3% for CC). Ethnic variation
in the COX-2 genotype distribution warrants additional comparative
studies with more patients to confirm our results. Several limitations
in our study need to be addressed. First, the sample size of the
malignant breast cancer cases was not large enough to detect a small
effect from low penetrating genes or SNPs. Second, inherent selection
bias cannot be completely excluded, because patients were enrolled
from the cancer hospitals and random controls were selected from a
similar population. Third, it has been well documented that regular
intake of NSAIDs may protect against breast cancer. Unfortunately,
in the present study, no data are available on personal factors such as
NSAID use and diet that potentially affect the COX-2 genotype.
In conclusion, our study demonstrated that COX-2
polymorphisms may conjointly contribute to risk of breast cancer
development in a North Indian population. Validation of these
findings with functional parameters and larger studies with more
rigorous study designs of other ethnic populations are needed.
Acknowledgment
This work was partly supported by the Department of Biotechnology (DBT), Govt of India, New Delhi under BTIS program. RK was a recipient of studentship from DBT under M. Biotech Teaching Program.
References
- Ali IU, Luke BT, Dean M, Greenwald P. Allellic variants in regulatory regions of cyclooxygenase-2: association with advanced colorectal adenoma. Br J Cancer. 2005;93(8):953-9.
- Appleby SB, Ristimäki A, Neilson K, Narko K, Hla T. Structure of the human cyclo-oxygenase-2 gene. Biochem J. 1994;302 ( Pt 3):723-7.
- Boland GP, Butt IS, Prasad R, Knox WF, Bundred NJ. COX-2 expression is associated with an aggressive phenotype in ductal carcinoma in situ. Br J Cancer. 2004;90(2):423-9.
- Campa D, Zienolddiny S, Maggini V, Skaug V, Haugen A, Canzian F. Association of a common polymorphism in the cyclooxygenase 2 gene with risk of non-small cell lung cancer. Carcinogenesis 2004;25(2):229-35.
- Chan G, Boyle JO, Yang EK, Zhang F, Sacks PG, Shah JP. Cyclooxygenase-2 expression is up-regulated in squamous cell carcinoma of the head and neck. Cancer Res. 1999;59(5):991-4.
- Cok SJ, Acton SJ, Morrison AR. The proximal region of the 3'-untranslated region of cyclooxygenase-2 is recognized by a multimeric protein complex containing HuR, TIA-1, TIAR, and the heterogeneous nuclear ribonucleoprotein U. J Biol Chem. 2003;278(38):36157-62.
- Cox DG, Pontes C, Guino E, Navarro M, Osorio A, Canzian F, et al. Polymorphisms in prostaglandin synthase 2/cyclooxygenase 2 (PTGS2/ COX2) and risk of colorectal cancer. Br J Cancer. 2004;91(2):339-43.
- Di Marco S, Hel Z, Lachance C, Furneaux H, Radzioch D. Polymorphism in the 3'-untranslated region of TNFalpha mRNA impairs binding of the post-transcriptional regulatory protein HuR to TNFalpha mRNA. Nucleic Acids Res. 2001;29(4):863-71.
- Eberhart CE1, Coffey RJ, Radhika A, Giardiello FM, Ferrenbach S, DuBois RN. Up-regulation of cyclooxygenase 2 gene expression in human colorectal adenomas and adenocarcinomas. Gastroenterology. 1994;107(4):1183-8.
- Gao J, Ke Q, Ma HX, Wang Y, Zhou Y, Hu ZB, et al. Functional polymorphisms in the cyclooxygenase 2 (COX-2) gene and risk of breast cancer in a Chinese population. J Toxicol Environ Health A. 2007;70(11):908-15.
- Gasparini G, Longo R, Sarmiento R, Morabito A. Inhibitors of cyclo-oxygenase 2: a new class of anticancer agents? Lancet Oncol. 2003;4(10):605-15.
- Hall-Pogar T, Zhang H, Tian B, Lutz CS. Alternative polyadenylation of cyclooxygenase-2. Nucleic Acids Res. 2005;33(8):2565-79.
- Hamid R, Singh J, Reddy BS, Cohen LA. Inhibition by dietary menhaden oil of cyclooxygenase-1 and -2 in N-nitrosomethylurea-induced rat mammary tumors. Int J Oncol. 1999;14(3):523-8.
- Howe LR, Crawford HC, Subbaramaiah K, Hassell JA, Dannenberg AJ, Brown AM. PEA3 is up-regulated in response to Wnt1 and activates the expression of cyclooxygenase-2. J Biol Chem. 2001;276(23):20108-15.
- Howe LR, Subbaramaiah K, Patel J, Masferrer JL, Deora A, Hudis C, et al. Celecoxib, a selective cyclooxygenase 2 inhibitor, protects against human epidermal growth factor receptor 2 (HER-2)/neu-induced breast cancer. Cancer Res. 2002;62(19):5405-7.
- Hu Z, Miao X, Ma H, Wang X, Tan W, Wei Q, et al. A common polymorphism in the 3'UTR of cyclooxygenase 2/prostaglandin synthase 2 gene and risk of lung cancer in a Chinese population. Lung Cancer. 2005;48(1):11-7.
- Langsenlehner U, Yazdani-Biuki B, Eder T, Renner W, Wascher TC, Paulweber B, et al. The cyclooxygenase-2 (PTGS2) 8473T>C polymorphism is associated with breast cancer risk. Clin Cancer Res. 2006;12(4):1392-4.
- Nakatsugi S, Ohta T, Kawamori T, Mutoh M, Tanigawa T, Watanabe K, et al. Chemoprevention by nimesulide, a selective cyclooxygenase-2 inhibitor, of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)- induced mammary gland carcinogenesis in rats. Jpn J Cancer Res. 2000;91(9):886-92.
- Papafili A, Hill MR, Brull DJ, McAnulty RJ, Marshall RP, Humphries SE, et al. Common promoter variant in cyclooxygenase-2 represses gene expression: evidence of role in acute-phase inflammatory response. Arterioscler Thromb Vasc Biol. 2002;22(10):1631-6.
- Park JM, Choi JE, Chae MH, Lee WK, Cha SI, Son JW, et al. Relationship between cyclooxygenase 8473T>C polymorphism and the risk of lung cancer: a case-control study. BMC Cancer. 2006;6:70.
- Ratnasinghe D, Tangrea J, Roth MJ, Dawsey S, Hu N, Anver M, et al. Expression of cyclooxygenase-2 in human squamous cell carcinoma of the esophagus; an immunohistochemical survey. Anticancer Res 1999;19:171-4.
- Ristimäki A, Sivula A, Lundin J, Lundin M, Salminen T, Haglund C, et al. Prognostic significance of elevated cyclooxygenase-2 expression in breast cancer. Cancer Res. 2002;62(3):632-5.
- Robertson FM, Parrett ML, Joarder FS, Ross M, Abou-Issa HM, Alshafie G, et al. Ibuprofen-induced inhibition of cyclooxygenase isoform gene expression and regression of rat mammary carcinomas. Cancer Lett. 1998;122(1-2):165-75.
- Rolland PH, Martin PM, Jacquemier J, Rolland AM, Toga M. Prostaglandin in human breast cancer: Evidence suggesting that an elevated prostaglandin production is a marker of high metastatic potential for neoplastic cells. J Natl Cancer Inst. 1980;64(5):1061-70.
- Romano M, Claria J. Cyclooxygenase-2 and 5-lipooxygenase converging functions on cell proliferation and tumor angiogenesis: Implications for cancer therapy. FASEB J. 2003;17:1986.
- Schmedtje JF Jr, Ji YS, Liu WL, DuBois RN, Runge MS. Hypoxia induces cyclooxygenase-2 via the NF-kappaB p65 transcription factor in human vascular endothelial cells. J Biol Chem. 1997;272(1):601-8.
- Schrey MP, Patel KV. Prostaglandin E2 production and metabolism in human breast cancer cells and breast fibroblasts. Regulation by inflammatory mediators. Br J Cancer 1995;72(6):1412-9.
- Siezen CL, van Leeuwen AI, Kram NR, Luken ME, van Kranen HJ, Kampman E. Colorectal adenoma risk is modified by the interplay between polymorphisms in arachidonic acid pathway genes and fish consumption. Carcinogenesis. 2005;26(2):449-57.
- Singh B1, Lucci A. Role of cyclooxygenase-2 in breast cancer. J Surg Res. 2002;108(1):173-9.
- Subbaramaiah K1, Norton L, Gerald W, Dannenberg AJ. Cyclooxygenase-2 is overexpressed in HER-2/neu-positive breast cancer: evidence for involvement of AP-1 and PEA3. J Biol Chem. 2002;277(21):18649-57.
- Szczeklik W, Sanak M, Szczeklik A. Functional effects and gender association of COX-2 gene polymorphism G-765C in bronchial asthma. J Allergy Clin Immunol. 2004;114(2):248-53.
- Tazawa R, Xu XM, Wu KK, Wang LH. Characterization of the genomic structure, chromosomal location and promoter of human prostaglandin H synthase-2 gene. Biochem Biophys Res Commun. 1994;203(1):190-9.
- Tsujii M, Kawano S, Tsuji S, Sawaoka H, Hori M, DuBois RN. Cyclooxygenase regulates angiogenesis induced by colon cancer cells. Cell. 1998;93(5):705-16.
- Tucker ON, Dannenberg AJ, Yang EK, Zhang F, Teng L, Daly JM, et al. Cyclooxygenase-2 expression is up-regulated in human pancreatic cancer. Cancer Res. 1999;59(5):987-90.
- Ulrich CM, Whitton J, Yu JH, Sibert J, Sparks R, Potter JD. PTGS2 (COX2) -765G > C promoter variant reduces risk of colorectal adenoma among nonusers of nonsteroidal anti-inflammatory drugs. Cancer Epidemiol Biomarkers Prev. 2005;14:616-9.
- Wolff H, Saukkonen K, Anttila S, Karjalainen A, Vainio H, Ristimäki A. Expression of cyclooxygenase-2 in human lung carcinoma. Cancer Res. 1998;58(22):4997-5001.
- Wülfing P, Diallo R, Müller C, Wülfing C, Poremba C, Heinecke A, et al. Analysis of cyclooxygenase-2 expression in human breast cancer: high throughput tissue microarray analysis. J Cancer Res Clin Oncol. 2003;129(7):375-82.
- Yang X, Hou F, Taylor L, Polgar P. Characterization of human cyclooxygenase 2 gene promoter localization of a TGF-beta response element. Biochim Biophys Acta. 1997;1350(3):287-92.
- Zhang X, Miao X, Tan W, Ning B, Liu Z, Hong Y, et al. Identification of functional genetic variants in cyclooxygenase-2 and their association with risk of esophageal cancer. Gastroenterology. 2005;129(2):565-76.