乳癌是全球婦女最常見的癌症之一，也是女性癌症死亡的主因。雌激素受體（ER）為乳房癌化的主要危險因子之一，也是診斷預後及治療的指標。雌激素受體存在兩種亞型(雌激素受體-a和雌激素受體-b)，每種亞型包含許多mRNA變異型（isoforms 及splice variants）。在乳房腫瘤組織中，已被證實會表現許多外顯子缺失之雌激素受體-a和雌激素受體-b mRNA變異型。推測這些 mRNA變異型所轉譯出的蛋白質，較野生型雌激素受體缺少某些功能性的區域，因而干擾野生型雌激素受體之訊息傳遞路徑。藉由偵測正常組織與乳房腫瘤組織中雌激素受體-a和雌激素受體-b mRNA變異型的表現量，可以證實他們在乳房癌化過程中所扮演的角色。依據我們先前的研究，在雌激素受體-a於密碼子-325處，基因型出現頻率在有淋巴結轉移與無淋巴結轉移的乳癌病人間有不同的分佈情形（χ2 =6.115，P=0.013）。在本研究中，我們建立即時性聚合酶連鎖反應的方法，對各雌激素受體-a/b mRNA變異型加以定量，並同時分析基因型。藉由此法，我們偵測乳房腫瘤組織及其對應之鄰近正常組織中雌激素受體-a密碼子-325與密碼子-594之核苷酸基因型，並定量雌激素受體-a/b mRNA表現量。我們的結果顯示，野生型雌激素受體-b mRNA的表現量在乳房腫瘤組織中約較其鄰近正常組織低4倍(Wilcoxon matched-paired test, n=30, p=0.001)。相反的，野生型雌激素受體-a、雌激素受體-a外顯子-3缺失、外顯子-5缺失及外顯子-7缺失等mRNA變異型的表現量在乳房腫瘤組織中與其鄰近正常組織並未呈現差異性(Wilcoxon signed-rank test, n=30, ER-a wild-type: p=0.644; ERa E3D: p=0.877; ERa E5D: p=0.781, ERa E7D: p=0.453)。在乳房腫瘤組織中，有表現雌激素受體或黃體激素受體者其雌激素受體-a mRNA變異型的表現量較未表現雌激素受體或黃體激素受體者高（Mann-Whitney test, p<0.001），而在Her-2/Neu未過度表現者較過度表現者高（Mann-Whitney test, ER-a wild-type, ERa E3D, ERa E5D: p<0.000；ERa E7D: p=0.001）。在有表現雌激素受體、有表現黃體激素受體或Her-2/Neu未過度表現者，其雌激素受體-b相較於雌激素受體-a的比值，在乳房腫瘤組織中也較其鄰近正常組織低（Wilcoxon signed-rank test, ER+: n=20, p=0.001; PR+: n=19, p=0.001; Her-2/Neu-: n=19, p=0.004）。值得注意的，我們發現在乳房腫瘤組織中雌激素受體-a密碼子325基因型會促進外顯子-3或外顯子-5缺失變異型的生成。本研究，首先提出雌激素受體-a/b mRNA變異型表現量與台灣地區乳癌之相關性，其結果顯示雌激素受體-a與雌激素受體-b間的調控在乳癌的癌化過程扮演重要角色。

　　Breast cancer is one of the most common neoplasms in women and is a leading cause of cancer related deaths worldwide. Estrogen receptor (ER) is a major risk factor for breast carcinogenesis, as well as a predictor for prognosis and response to therapy. There are two subtypes of estrogen receptor (ER-a and ER-b), with each mRNA encompassing several isoforms and splice variants. Altered expression of exon-skipping ER-a and ER-b mRNA variants has been reported in breast tumor tissues. The putative proteins that are encoded by these variant mRNAs would therefore be missing some functional domains of the wild-type ERs, and might interfere with wild-type ERs signaling pathways. The detection of ER-a and ER-b mRNA variants in both normal and neoplastic breast tissues may identify their possible role in the development of mammary cancer. In our previous study, we had found that genotyping frequencies exhibited different distributions in the presence and absence of lymph node metastasis, with a statistical significance for ER-a codon 325 (χ2 =6.115, p=0.013). In this study, we established a real-time PCR method to quantify the ER-a/b mRNA expression level and to analyze the genotypes simultaneously. By the current method, we determined ERa325 and ERa594 genotypes and quantified the exon-skipping ER-a/b mRNA variants in breast tumor tissues and their matched normal tissues. The results revealed that 4 folds lower ER-b wild-type mRNA was found in breast tumors as compared with their matched adjacent normal breast tissues (Wilcoxon matched-paired test, n=30, p=0.001). On contrary, there are no significant difference of ER-a wild-type, ERa E3D, ERa E5D, and ERa E7D mRNAs between breast tumors and their adjacent normal tissues (Wilcoxon signed-rank test, n=30, ER-a wild-type: p=0.644; ERa E3D: p=0.877; ERa E5D: p=0.781, ERa E7D: p=0.453). The expression level of ER-a mRNA variants had a positive correlation with the expression of ER and PR（Mann-Whitney test, p<0.001）, but a negative correlation with the expression of Her-2/Neu in breast tumors（Mann-Whitney test, ER-a wild type, ERa E3D, ERa E5D: p<0.001；ERa E7D: p=0.001）. The patients in subgroups of ER+, PR+, or Her-2/Neu-, the ratio of ER-b wild-type to ER-a wild-type was also decreased in breast tumors as compared with their matched adjacent normal breast tissues（Wilcoxon signed-rank test, ER+: n=20, p=0.001; PR+: n=19, p=0.001; Her-2/Neu-: n=19, p=0.004）. Remarkably, we found that the ERa325 genotypes in tumor may contribute to the exon 3 and exon 5 skipping. This study first showed the expression of ER-a/b mRNA variants with the clinical relevance of breast cancer in Taiwan. The results suggest that the regulation between ER-a and ER-b must play some important roles in the progression of breast tumors.

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