A Molecular Epidemiology Study On The Association Of EGF And HTERT Genes Polymorphisms And The Susceptibility Of Breast Cancer

Breast cancer is the most common malignancy among women, accounting for nearly one in three cancers diagnosed among women in the United States. Although the incidence rate of breast cancer in China is about one-third of that in the United States, it has been significantly increasing in the last two decades in both urban and rural areas, especially in big cities as Shanghai and Beijing. However, the exact molecular mechanisms to breast cancer are still unclear. It is well accepted that interaction of environmental factors and genetic factors may contribute to the development of breast cancer. The individuals with different genetic background have different risk of breast cancer. So, identifying the breast cancer susceptibility genes is the most important task in recognizing high risk population. It is well known that the mutations in human family breast cancer susceptibility genes, BRCA1/2, are strong risk factors to breast cancer, but it only account for less than 5% of all breast cancer cases. Thus, it is crucial to investigate other genetic risk factors of breast cancer in general population. Mounting evidence indicates high level of endogenous estrogen is believed to contribute to the etiology of breast cancer. Epidermal growth factor (EGF), a potent mitogenic peptide, is in possession of estrogen-like property and also plays important role in breast carcinogenesis. Over-expression of EGF may increase proliferation, inhibit apoptosis and enhance the invasiveness of breast cancer cells by activating its signal transduction pathways. Studies showed the polymorphisms in the promoter of EGF gene are associated with plasma EGF level and risk of cancer. Meanwhile, EGF up-regulates telomerase reverse transcriptase (hTERT) activity and regulates telomere length maintenance and promotes cell proliferation uncontrolled, eventually leads to cancer. hTERT mRNA is absent in most normal human somatic cells, but is detected in many human cancers, including breast cancer. Thus, we conducted a case-control study aiming to investigate the association of plasma EGF levels and SNPs of EGF and hTERT genes with breast cancer risk in Chinese populations.Part IEGF Promoter SNPs, Plasma EGF levels and Risk of BreastCancer in Chinese WomenEGF expression was suggested to be regulated by EGF promoter activity, suggesting the variants in EGF promoter region may affect the EGF expression in diffrent individuals, eventually influence the susceptibility to cancer. Shahbazi et al. found the variant of G61A in EGF promoter region led to a decreased EGF production in peripheral blood mononuclear cells and decreased susceptibility of malignant melanoma. Thus, the polymorphisms in EGF promoter may influence the plasma EGF level and contribute to inter-individual variability in susceptibility to breast cancer.The aim of this case-control study is to investigate the associations of plasma EGF levels and three EGF promoter SNPs (G61A, G-1380A and A-1744G) with breast cancer risk and the modification effects of EGF promoter SNPs on plasma EGF levels. This case-control study included 629 histologically confirmed incident breast cancer patients and 694 cancer-free controls frequency-matched for age and area. We genotyped the three promoter polymorphisms by PCR-RFLP (PCR-Restriction Fragment Length Polymorphism) and PCR-PIRA (PCR-Primer Introduced Restriction Analysis) method. In this case control study, the plasma EGF concentration was measured with ELISA (Enzyme-Linked Immunosorbnent Assay). In addition, genotyping was performed blindly and 10% of the samples were randomly selected for repeated assays. Finally, a total of 604 (96.0%) breast cancer cases and 654 (94.2%) controls were successfully genotyped.In this case-control study, we did not find any significant associations between the three EGF polymorphisms (G61A, G-1380A and A-1744G) and risk of breast cancer even after adjusting by confounder factors in multifactor logistic analysis. However, we found the mean plasma EGF levels in breast cancer patients (249.06±197.54pg/ml) were significantly lower than those in controls (982.41±375.57pg/ml, P<0.001). According to the quartile levels in the controls, the risks of breast cancer were decreased compared with the lowest quartile of EGF, and the trend of increase was significant (x~2=474.35, P<0.001). In addition, there was a significant difference of plasma EGF levels among different genotypes carriers of the G-1380A locus in controls (P=0.007). The individuals EGF-1380AA had significantly higher plasma EGF levels than -1380GG carriers did (1308.87 pg/ml vs 946.87pg/ml, P=0.003). These findings indicated that plasma EGF levels served as a protective marker against breast cancer in our study and EGF G-1380A variant might be a modifier on it.Part IIA tandem repeat of human telomerase reverse transcriptase(hTERT) and risk of breast cancer development andmetastasis in Chinese womenStudies showed a polymorphic tandem repeat minisatellite (termed MNS16A) in the downstream of hTERT gene was demonstrated to regulate the expression of hTERT rnRNA level, influence telomerase activity, and eventually may contribute to inter-individual variability in susceptibility to breast cancer. So, we hypothesized that the MNS16A variant may be associated with breast cancer risk and phenotypes in Chinese women. This case-control study included 1029 histologically confirmed incident breast cancer patients and 1107 cancer-free controls frequency-matched for age and area. We genotyped the MNS16A variant by PCR method. Genotyping was performed blindly and 10% of the samples were randomly selected for repeated assays. Finally, a total of 1006 (97.8%) cancer cases and 1095 (99.3%) controls were successfully genotyped.In this case-control study, we found a significantly increased risk of breast cancer associated with the MNS16A variant genotypes (302/271, 302/243 and 243/243) and the effects were more evident among the older women (≥50), postmenopausal women, and individuals with family history of cancer, with earlier menarche age (<16), with older age at first live birth (≥25). In breast cancer cases, 302/271 genotype was associated with an increased risk for axillary lymph node metastasis (adjusted OR=2.13, 95%CI=1.05-4.33).These results supported that hTERT-MNS16A variant might be associated with breast cancer development and metastasis in Chinese population.