在美国，乳腺癌是所有女性中第二大癌症死亡原因，也是黑人女性中第一大癌症死亡原因。通过对组织样本进行免疫组织化学染色，可以评估乳腺癌受体配置文件，从而预测结果和指导病人治疗方向。大约80％的新诊断乳腺癌是激素受体（HR）阳性，即雌激素受体（ER）和/或孕激素受体（PR）阳性。 ER阳性疾病的患者可以接受针对ER的治疗; 然而，用组织活检标本的免疫组织化学染色评估ER表达有几个限制，包括取样误差，假阴性结果，挑战性或无法接近的活检部位以及无法同时和连续评估所有转移部位以确定空间和/或时间上的ER异质性。 2020年5月，在几十年的研究之后，美国食品和药物管理局批准了PET放射性示踪剂氟18（18F）氟雌二醇（FES）用于ER阳性复发性或转移性乳腺癌患者的临床使用作为活检的辅助。 FES结合在ER表达细胞的细胞核中的ER上，使得ER表达得以进行全身在体评估。 本文主要介绍美国批准使用FES的用途，包括鉴定确认性活检的目标病变，评估活检证实的ER阳性疾病在体内情况以及评估空间和时间ER异质性。 FES是精准医学的一个例子，已被利用来优化乳腺癌患者的护理。 ©RSNA，2023。 本期的邀请评论由福勒提供。本文的提问内容可通过在线学习中心获得。

In the United States, breast cancer is the second leading cause of cancer death in all women and the leading cause of cancer death in Black women. The breast cancer receptor profile, assessed with immunohistochemical staining of tissue samples, allows prediction of outcomes and direction of patient treatment. Approximately 80% of newly diagnosed breast cancers are hormone receptor (HR) positive, which is defined as estrogen receptor (ER) and/or progesterone receptor (PR) positive. Patients with ER-positive disease can be treated with therapies targeting the ER; however, the assessment of ER expression with immunohistochemical staining of biopsy specimens has several limitations including sampling error, false-negative results, challenging or inaccessible biopsy sites, and the inability to synchronously and serially assess all metastatic sites to identify spatial and/or temporal ER heterogeneity. In May 2020, after decades of research, the U.S. Food and Drug Administration approved the PET radiotracer fluorine 18 (18F) fluoroestradiol (FES) for clinical use in patients with ER-positive recurrent or metastatic breast cancer as an adjunct to biopsy. FES binds to the ER in the nucleus of ER-expressing cells, enabling whole-body in vivo assessment of ER expression. This article is focused on the approved uses of FES in the United States, including identification of a target lesion for confirmatory biopsy, in vivo assessment of biopsy-proven ER-positive disease, and evaluation of spatial and temporal ER heterogeneity. FES is an example of precision medicine that has been leveraged to optimize the care of patients with breast cancer. © RSNA, 2023 See the invited commentary by Fowler in this issue. Quiz questions for this article are available through the Online Learning Center.