Assessing mifepristone's effects on endometrial tissue in women with BRCA mutations: A randomised clinical trial

Background: The endometrium, regulated by steroid hormones, is particularly susceptible to disease under imbalanced hormonal conditions. Progesterone regulates cell growth differently across tissues, acting as a pro-tumorigenic agent in the breast while serving as a tumor suppressor in the endometrium by countering the effects of oestradiol. Progesterone receptor modulators like mifepristone may prevent breast cancer formation but raise concerns about unopposed oestradiol exposure in the endometrium. This study examines mifepristone's impact on the endometrium, particularly its potential link to endometrial carcinogenesis in BRCA mutation carriers, who have DNA repair and replication vulnerabilities. Methods: This study was part of a randomised, double-blind, placebo-controlled trial in which pre-menopausal women carrying BRCA1 or BRCA2 mutations were assigned to a three-month treatment with either mifepristone (50 mg) or a non-hormonal comparator (TrioB) every second day. Endometrial biopsies were collected pre- and post- treatment, processed, and analysed for changes in endometrial thickness, cellular composition, methylation patterns, and gene expression profiles. Compliance and safety monitoring were rigorously maintained. Results: Mifepristone treatment led to amenorrhea in all treated participants, consistent with its inhibition of ovulation. Ultrasound showed a non-significant increase in endometrial thickness post-treatment. Cellular analysis indicated a shift in composition, with a reduction in epithelial cells and an increase in fibroblast levels, suggesting that endometrial thickening may primarily reflect stromal expansion rather than epithelial proliferation. This distinction is clinically important, as epithelial proliferation is more closely associated with carcinogenesis. DNA methylation analysis revealed no significant alterations in the TCGA-EC methylation index, and gene expression profiling showed no significant elevation in carcinogenesis-related genes. Conclusions: Mifepristone treatment in BRCA mutation carriers does not significantly impact methylation or gene expression profiles associated with endometrial carcinogenesis. The findings support from the safety of short-term mifepristone use in this population, although long-time safety of mifepristone use in BRCA mutation carriers will be needed. Overall design: Molecular analysis involved RNA and DNA extraction from 15 paired biopsies, RNA sequencing using the Smart-seq2 protocol, and methylation profiling with Illumina Human Methylation EPIC arrays. RNA-seq data were processed using Partek Flow, identifying genes of interest, while DNA methylation data supported the development of an endometrial cancer index. This index, trained on TCGA UCEC data, demonstrated robust accuracy and was applied to the study dataset to explore its diagnostic utility.

背景：子宫内膜（endometrium）受类固醇激素调控，在激素失衡状态下极易发生病变。孕酮（Progesterone）在不同组织中对细胞生长的调控作用存在差异：在乳腺中可发挥促肿瘤发生作用，而在子宫内膜中则通过拮抗雌二醇（oestradiol）的效应充当肿瘤抑制因子。米非司酮（mifepristone）等孕激素受体调节剂可预防乳腺癌发生，但可能引发子宫内膜部位雌二醇暴露不受拮抗的安全隐患。本研究探讨米非司酮对子宫内膜的影响，尤其是其与BRCA突变携带者（BRCA mutation carriers）子宫内膜癌变（endometrial carcinogenesis）的潜在关联——这类人群存在DNA修复与复制缺陷。

方法：本研究为一项随机双盲安慰剂对照试验（randomised, double-blind, placebo-controlled trial）的子研究，纳入携带BRCA1或BRCA2突变的绝经前女性，按方案每隔日接受为期3个月的米非司酮（50mg）治疗或非激素类对照药物（TrioB）治疗。分别于治疗前后采集子宫内膜活检样本，对其进行处理后分析子宫内膜厚度、细胞组成、甲基化模式及基因表达谱的变化，并严格开展依从性与安全性监测。

结果：米非司酮治疗使所有受试者均出现闭经（amenorrhea），这与其抑制排卵的作用一致。超声检查显示，治疗后子宫内膜厚度呈非显著性升高。细胞分析表明细胞组成发生改变：上皮细胞（epithelial cells）数量减少，成纤维细胞（fibroblast levels）水平升高，提示子宫内膜增厚主要反映间质扩张而非上皮增殖——这一区分具有重要临床意义，因上皮增殖与癌变的关联更为紧密。DNA甲基化分析（DNA methylation analysis）显示，TCGA-EC甲基化指数（TCGA-EC methylation index）无显著变化；基因表达谱分析亦未发现致癌相关基因出现显著性上调。

结论：米非司酮用于BRCA突变携带者治疗时，不会显著改变与子宫内膜癌变相关的甲基化或基因表达谱特征。本研究结果支持该人群短期使用米非司酮的安全性，但仍需开展长期用药安全性的相关研究。

总体研究设计：本研究的分子分析环节包含：从15份配对活检样本中提取RNA与DNA；采用Smart-seq2协议进行RNA测序；利用Illumina人类甲基化EPIC芯片（Illumina Human Methylation EPIC arrays）开展甲基化分型。RNA测序数据通过Partek Flow进行处理以筛选目标基因；DNA甲基化数据用于构建子宫内膜癌指数。该指数基于TCGA UCEC数据训练得到，具备良好的诊断准确性，随后被应用于本研究数据集以探索其诊断效用。