During the past 25 years or so a number of studies have been carried out to address the hypothesis that the ratio of 2-hydroxyestrone (2-hydroxy-E1) to 16α-hydroxyestrone (16α-hydroxy-E1) is associated with breast cancer risk. The rationale for this hypothesis is based on data from studies that suggest a tumorigenic and genotoxic effect of 16α-hydroxy-E1 and a protective effect of 2-hydroxy-E1 regarding breast cancer risk. The adverse effect of 16α-hydroxy-E1 has been attributed to its potential to form covalent adducts with macromolecules. Initial studies used radiometric assays and enzyme immunoassays to test the hypothesis. However, concerns about the accuracy of these assays led to the development of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay that is capable of measuring 5 unconjugated and 15 conjugated endogenous estrogens, which include 2- and 16-hydroxylated estrogen metabolites, in serum or urine. The conjugated estrogens are quantified following a deconjugation (hydrolysis) step to remove the sulfate and glucuronide groups. Epidemiologic studies have been using the LC-MS/MS assay to determine whether there is an association between breast cancer risk and the ratio of the sum of the concentrations of metabolites in the 2-hydroxylated estrogen pathway and in the 16-hydroxylated estrogen pathway. However, the validity of the pathways as biomarkers was not evaluated. The 16-hydroxylated estrogen pathway includes estriol, 16-epiestriol, 17-epiestriol and 16-ketoestradiol, in addition to 16α-hydroxy-E1. However, with the exception of 16α-hydroxy-E1, there is no evidence that any of the other estrogens in the pathway have tumorigenic or genotoxic properties, and they do not form covalent adducts with macromolecules. Another deficiency in the epidemiological studies pertains to the accuracy of estrogen metabolite measurements obtained after the hydrolysis step in the LC-MS/MS assays. No validation was performed to demonstrate that a constant efficiency of hydrolysis is found for all the different structural forms of sulfated and glucuronidated conjugates. Other deficiencies in the assays include the need for greater sensitivity so that the very low concentrations of unconjugated 2-hydroxy-E1, 2-hydroxy-E2, and 16α-hydroxy-E1 can be measured in serum. There is also a need to develop assays to measure intact forms of conjugated estrogens in both serum and urine, particularly the sulfates and glucuronides of 2-hydroxylated, 2-methoxylated, and 16α-hydroxylated E1 and E2. This will avoid inaccuracies that stem from hydrolysis procedures. Improvements in LC-MS/MS assay methodology to obtain accurate measurements of unconjugated and conjugated 2-hydroxylated, 2-methoxylated, and 16α-hydroxylated estrogen metabolites are needed. This should provide valuable data for testing the 2-/16α-hydroxylated estrogen-breast cancer risk hypothesis.

中文翻译：

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2- /16α-羟基雌激素比-乳腺癌风险假说：证据不足。

在过去的25年左右的时间里，已经进行了许多研究来解决以下假设：2-羟基雌酮（2-羟基-E1）与16α-羟基雌酮（16α-羟基-E1）的比例与患乳腺癌的风险有关。该假设的基本原理是基于研究的数据，这些数据表明16α-羟基-E1的致癌和遗传毒性作用以及2-羟基-E1对乳腺癌风险的保护作用。16α-羟基-E1的不利影响归因于其与大分子形成共价加合物的潜力。最初的研究使用放射测定法和酶免疫测定法来检验假设。然而，对这些测定法准确性的担忧导致了液相色谱-串联质谱（LC-MS / MS）测定法的发展，该测定法能够测量5种未结合的和15种结合的内源性雌激素，其中包括2和16羟基化的雌激素代谢物，在血清或尿液中。在去结合（水解）步骤以除去硫酸根和葡糖醛酸根基团之后，对缀合的雌激素进行定量。流行病学研究一直在使用LC-MS / MS分析来确定乳腺癌风险与2-羟基化雌激素途径和16-羟基化雌激素途径中代谢物浓度之和之比之间是否存在关联。但是，没有评估这些途径作为生物标志物的有效性。16-羟基化雌激素途径包括雌三醇，16-庚三醇，除16α-羟基-E1外，还有17-庚三醇和16-酮雌二醇。但是，除16α-羟基-E1外，没有证据表明该途径中的任何其他雌激素都具有致癌或遗传毒性性质，并且它们不会与大分子形成共价加合物。流行病学研究的另一个不足之处是在LC-MS / MS分析中水解步骤后获得的雌激素代谢物测量的准确性。没有进行验证以证明对于硫酸盐化和葡萄糖醛酸化的缀合物的所有不同结构形式都发现了恒定的水解效率。该测定法的其他缺陷包括需要更高的灵敏度，以便可以在血清中测量非常低浓度的未结合的2-羟基-E1、2-羟基-E2和16α-羟基-E1。还需要开发测定以测量血清和尿液中完整形式的结合雌激素的测定法，特别是2-羟基化，2-甲氧基化和16α-羟基化的E1和E2的硫酸盐和葡糖醛酸。这将避免由于水解程序而产生的不准确性。需要改进LC-MS / MS分析方法，以准确测量未结合和结合的2-羟基，2-甲氧基和16α-羟基雌激素代谢物。这应该为测试2- /16α-羟基化雌激素-乳腺癌风险假说提供有价值的数据。需要改进LC-MS / MS分析方法，以准确测量未结合和结合的2-羟基，2-甲氧基和16α-羟基雌激素代谢物。这应该为测试2- /16α-羟基化雌激素-乳腺癌风险假说提供有价值的数据。需要改进LC-MS / MS分析方法，以准确测量未结合和结合的2-羟基，2-甲氧基和16α-羟基雌激素代谢物。这应该为测试2- /16α-羟基化雌激素-乳腺癌风险假说提供有价值的数据。