| Background and PurposeBrest cancer is a kind of malignancy on mammary glands and duct epithelial cells. According to the relevant statistics form WHO and national Ministry of Health, breast cancer has been an important disease which threats the health of women in our country. And it also shows younger trend in the incidence of breast cancerBreast cancer is a disease induced by comprehensive factors, including age, region, reproductive factors, environmental factors, psycho-social factors and so on. The current study shows that alcohol consumption, smoking, history of breast disease, stressful life events, and troubles, anxiety, fatigue and depression are all risk factors closely related with breast cancer, while early age pregnancy, high number of pregnancies, and long-term high-intensity physical exercise are all protective factors of breast cancer. What's more, the difference on the level of estrogen receptor also inference the susceptibility of breast cancer.Breast cancer is not only a result of environmental factors but also affected by genetic susceptibility. It is a kind of diseases induced by interaction of environmental and genetic factors, which leads to turbulence of cell cycle and uncontrolled cell proliferation. There is strict cell cyclesequencing from G1-S-G2-M, among which G1-S check point is especially important. If this check point is spanned, cell cycle will carry through without stimulation of exterior signal. p53 pathway and cell cycle related regulating protein play an important role at the G1-S check point. Among them, p53 codon72 Arg/Pro, intron 3 16bp induplication, intron 6 G/A, p21 70C/, CCND1 A871G polymorphisms attract more attention currently.The purpose of this population-based case-control study is to explore the association between genetic polymorphism in GI-S cell cycle regulation and the susceptibility to breast cancer on a population level by using field epidemiology and molecular epidemiology methods comprehensively, in order to clarifying specific genetic susceptibility marks of breast cancer, providing research evidence for genetic susceptibility to breast cancer on a population level, and serving crowd prevention and clinical treatment ultimately.Material and MethodsIn this population-based case-control study, a colorectal cancer screening cohort in Jiashan County, Zhejiang Province with 64693 persons enrolled in which covered 10 towns and was established during 1989 to 1990 was treated as the study population. 84 of 118 prevalent patients of primary breast cancer diagnosed from May 1990 to May 2005 in the cohort, eliminating the missing follow-up cases and refusing investigation cases, made up of the case group. According to age and sex distributions of the cohort, 280 persons were selected out as controls by stratified sampling, and actually 269 persons both accepted the investigation and provided effective blood samples. All of the controls alive never had neoplasm.A constructed questionnaire elicited information on the demographic condition, life styles and habits, dietary habits and categories, and past disease histories. All subjects were interviewed face-to-face by trained interviewers. Intake quantities of all common kinds of foods were obtained by asking subjects per time intake and intake frequencies of foods, and uniform-made food models were used to assist the food investigation.Also with subjects' permission, a sample of venous blood (5ml) was taken at the same time of interview, which was separated into two sections of 2ml blood with sodium citrate anticoagulation and 3ml blood without anticoagulation to gain blood serum. All blood samples were stored at -60 centigrade degrees(°C) refrigerator for long-term conservation. Genome DNA was extracted from leucocytes by improved salt out method. Genotypes of p53 codon 72 Arg/Arg, intron 6 G/A polymorphisms, and p21 70C/T, CCND1 870A/G were detected by PCR-restriction lengthen polymorphism (PCR-RFLP). The p53 intron 3 16bp induplication was detected by directly electrophoresing PCR products on agarose gels.All questionnaires were uniformly coded, and then input into computer for double times. After revising and correcting the data, statistical analysis was carried out. Distributional characteristics of qualitative variables between cases and controls were analyzed by x~2 tests, and a non-conditional Logistic model was used for estimations of OR values for breast cancer of related study factors, chi-square trend test for judging dose-reaction relationship. The Hardy-Weinberg equilibrium test in control group was finidhed by x~2 goodness-of-fit test. EH Linkage Software 1.2 was used to identify the linkage disequilibrium. And the interaction model was applied for analysis of gene-gene and gene-environment interaction to breast cancer. All analyses were performed with SPSS for Windows 13.0, EH Linkage Software 1.2and Excel 2003.Results1. Environmental exposure and breast cancerIn our study, the distribution of age and marital status had no difference between cases and controls, while occupation and education showed uneven distribution between cases and controls, with x~2 =12.17 and 17.14, P=0.11 and 0.00 respectively, which indicated statistical significance. After being adjusted by age, non-conditional Logistic regression analysis suggested that subjects with education degrees of junior middle school had a statistically significant increased risk of breast cancer with an OR value of 3.47(95%CI: 1.50-8.04, P<0.01), however, farmers were at a statistically significant decreased risk of breast cancer with an OR value of 0.33(95%CI:0.19-0.56, P<0.05).Cigarette smoking was associated with increased risk of breast cancer distinctly, with an OR value of 3.70 (95%CI: 1.03-13.29, P<0.05). But there was no statistical significance between drinking, tea and breast cancer. Also, bad mood was a risk factor for breast cancer (OR=3.03, 95%CI: 1.60-5.76, P<0.01). Compared with people without benign breast disease, elevation of breast cancer risk was most pronounced among people with a history of benign disease (OR=8.93, 95%CI: 2.00-39.85, P<.05).For dietary factors, subjects prefer to fried or pickled fish had a statistically significant increased risk of breast cancer with OR value of 1.86 (95%CI: 1.06-3.25, P<0.05) and 2.08 (95%CI: 1.20-3.61, P<0.01) respectively.For factors about reproduction period of woman, menarche age, total number of pregnancies and time of lactation all showed uneven distribution between cases and controls. The mean menarche age of cases was 0.7 year earlier than controls (P=0.005). While the mean total number of pregnancies of cases was 0.5 times more than controls (P=0.001), and showed a decreasing trend of breast cancer risk as the total number of pregnancies increased. What's more, lactation also had a protective effect to breast cancer with mean lactation time of controls 11.8 months more than cases (P=0.004).2. Genetic polymorphisms and breast cancerAnalysis about p53 codon 72, intron 6, intron 3, p21 C70T and CCND1 A870G all showed no statistically significant association between these genetic polymorphisms and breast caner.Linkage disequilibrium of p53 haplotypes was observed in control group, but not in case group. A-Arg-G and A-Pro-G were two haplotypes mostly observed, and the total percentage of which were 93.2% and 90.3% in cases and controls respectively.3. Gene-gene interaction and breast cancerNo statistically significant interaction to breast caner between p53 codon 72, intron 6, intron 3, p21 C70T and CCND1 A870G were observed in this study.4. Gene-environment interaction and breast cancerAmong subjects whose menarche age was lower than 16, the gene types of p53 codon 72 Arg /Arg and intron 6 GG were linked with decreased breast cancer risk, with P value higher than 0.05. However, analysis by interaction model showed that no statistically significant interaction to breast caner between menarche age and p53 genetic polymorphism were observed (P>0.05). In a word, gene-environment interaction to breast caner could not be confirmed in this study and further research was in need.ConclusionAccording to this population-based case-control study, cigarette smoking, bad mood, prefer to fried or pickled fish, and with benign breast disease are all risk factors for breast cancer, while menarche age, total number of pregnancies and time of lactation are factors distributing unevenly between cases and controls groups, that indicates certain association between such factors and susceptibility of breast cancer but should be confirmed further.However, analysis about p53 codon 72, intron 6, intron 3, p21 C70T and CCND1 A870G are all showed no statistically significant association between these genetic polymorphisms and breast caner. So they could not be considered as independent predictors to breast cancer yet. As to analysis of gene-gene and gene-environment interaction, the results also have no statistical significance, which indicates further research with larger sample size should be conducted in the near future. |
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