| 摘要: | 乳癌為全球婦女最常見的癌症，臺灣近二十年來乳癌標準化發生率於女性惡性腫瘤發生率中高居首位，且平均發病年齡與診斷年齡皆低於西方國家，顯示臺灣女性乳癌有年輕化的趨勢。微型核醣核酸(microRNA, miRNA)為普遍存在於動物、植物及病毒中的一種內生性機制，其結構約為17~25個核苷酸、且不會轉譯出蛋白的小片段核醣核酸，對於體內許多調控機制相當重要。近年許多研究指出，miRNA異常表現與腫瘤生成息息相關，在癌症中可能扮演腫瘤促進者或抑制者的角色，其中位於miRNA上的變異也可能影響miRNA表現。本研究團隊先前利用TaqMan microRNA Assay結果篩選出microRNA-27a (miR-27a)血清中表現量在早發型及晚發型乳癌病患之間有顯著差異，過去文獻也指出，miR-27a在乳癌腫瘤組織相較於正常組織有異常表現之情形，並且在乳癌發展過程中扮演著腫瘤促進者的角色。另有文獻提及，在miR-27a前驅體的序列上有一個常見的單核苷酸多形性(single nucleotide polymorphism, SNP)，此基因多形性可能與miR-27a表現相關，進而影響癌症的易感性與臨床結果。故本研究目的為探討miR-27a基因多形性(rs895819 A→G)及miR-27a表現量，以及乳癌危險因子與早發型、晚發型乳癌之相關性。
本研究為以醫院為基礎之病例對照研究，研究對象來自北醫、萬芳、雙和、國泰四所醫院之乳癌確診病患，包含124位≤40歲早發型乳癌及277位≥55歲晚發型乳癌個案，並經由年齡頻率配對後分別配對出124位、277位健康對照之研究對象。資料收集為利用結構式問卷且標準化流程收集研究對象之基本人口學、疾病史及乳癌相關危險因子等資訊。基因多形性分析利用聚合酶連鎖反應-限制片段長度多形性(Polymerase chain reaction-Restriction fragment length polymorphism, PCR-RFLP)，另外也利用即時定量聚合酶連鎖反應(Quantitative Real Time Polymerase Chain Reaction; qRT-PCR)，並搭配SYBR GREEN方法測量研究對象血漿中miR-27a表現量。統計方法使用t檢定及卡方檢定比較病例組與對照組間連續或類別變項之差異，無母數分析則用來檢定miR-27a表現量在兩組或三組間是否具有差異，並使用羅吉斯迴歸分析miR-27a基因多形性及乳癌危險因子與早發型、晚發型乳癌之相關性。
本研究結果顯示，曾有菸害暴露者會顯著增加早發型與晚發型乳癌之風險。基因多形性與危險因子綜合分析發現，曾有菸害暴露且攜帶miR-27a rs895819危險基因型者，罹患早發型與晚發型乳癌風險皆顯著較高，並且具有顯著劑量效應關係。然而，本研究並未發現miR-27a表現量在早發型與晚發型乳癌之間具有顯著差異；miR-27a rs895819基因多形性僅在乳癌病例組中觀察到AG基因型之miR-27a表現量顯著低於AA+GG基因型。
本研究發現菸害暴露為乳癌之重要危險因子。曾有菸害暴露且同時攜帶miR-27a rs895819危險基因型者，有較高罹患早發型與晚發型乳癌的風險，且罹患晚發型乳癌之風險高於早發型乳癌。
關鍵字：早發型乳癌、晚發型乳癌、微型核醣核酸、miR-27a、基因多形性
Breast cancer is the most common female malignancy in the world and also in Taiwan. During the past two decades, female breast cancer had the highest age-standardized incidence rate than other cancers in Taiwan, and the average onset age and age at diagnosis are lower than Western countries, showing that the younger pattern of female breast cancer in Taiwan is an important issue of public health. MicroRNA (miRNA) are single-stranded RNAs of 19-25 nucleotides in length that are generated from endogenous hairpin-shaped transcripts, and was shown to play an important role in several human cancers. Some miRNA may function as oncogenes or tumor suppressors. Furthermore, genetic variants located within miRNA may affect aberrant expression of miRNA. Our previous data showed that the expression of miR-27a in serum was significantly different between early-onset and late-onset breast cancer patients. Other previous studies implicated that the expression of miR-27a was significantly up-regulated in breast cancer tissue, and might be an oncogenic miRNA which was involved in breast cancer carcinogenesis. Moreover, there is a common single nucleotide polymorphism (SNP) located on precursor of miR-27a that could alter expression of miR-27a and further influence breast cancer susceptibilities and clinical outcomes. Therefore, the purpose of this study was to evaluate the association between genetic polymorphism and the expression of miR-27a (rs895819 A→G) with early-onset and late-onset breast cancer.
A total of 124 early-onset and 277 late-onset breast cancer patients were recruited from TMU, Wan-Fan, Shuang-Ho and Cathay General Hospitals in Taiwan, and there were 124 and 277 age-matched healthy controls for early-onset and late-onset group respectively. All subjects were interviewed by well-trained research assistants using structural questionnaire to including demographic characteristics data and breast cancer risk factors. We genotyped the genetic polymorphism of miR-27a by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The level of miR-27a of plasma were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Student t test, Chi-Square (χ^2) test and nonparametric statistics were used to compared differences between cases and controls. Logistic regression was used to assess the association between genetic polymorphism of miR-27a and early-onset and late-onset breast cancer.
Our study showed that tobacco exposure were associated with a significantly increasing risk of early-onset and late-onset breast cancer. Besides, high risk genotype of miR-27a rs895819 and those with tobacco exposure were associated with a significantly increasing risk of early-onset and late-onset breast cancer. However, we didn’t found that the expression of miR-27a were significantly between early-onset and late-onset breast cancer patients. The expression of miR-27a of rs895819 AG genotype was lower than that of AA+GG genotypes only in breast cancer patients.
In conclusion, tobacco exposure is an important risk factor of early-onset and late-onset breast cancer. Study subjects with tobacco exposure and also with high risk genotypes of miR-27a rs895819 were affected with increasing risk of early-onset and late-onset breast cancer, and the risk effect of late-onset breast cancer was higher than that of early-onset breast cancer.
Keywords: Early-onset, Late-onset, Breast cancer, microRNA, miRNA, miR-27a, Genetic Polymorphism |
