乳腺癌治疗中，人表皮生长因子受体2（HER2）的评估至关重要。对于复发病例，治疗决策通常依赖于初发肿瘤状态。然而，越来越多的证据表明肿瘤呈现动态变化，多达10％的乳腺癌在进展过程中改变其初始状态。目前对于这些变化是反映疾病的生物学演进还是与初发肿瘤的异质性有关仍存在争议。重复进行乳腺癌进展过程中的HER2评估对于有效的抗HER2药物的不断提供非常重要。为满足这一需求，循环生物标志物如循环肿瘤细胞（CTCs）和游离循环肿瘤DNA（ctDNA）提供了安全、可重复评估HER2状态的潜力。本章概述了CTCs和ctDNA中HER2测试的当前方法，并回顾了研究其对乳腺癌患者的预后和预测价值以及该领域的最新进展。版权所有 © 2023 Elsevier Inc. 发布。

Human Epidermal growth factor Receptor 2 (HER2) assessment is crucial for breast cancer treatment. Therapeutic decisions for recurrent cases often rely on primary tumor status. However, mounting evidence suggests that tumors show dynamic changes and up to 10% of breast cancer modify their initial status during progression. It is still debated whether these changes reflect a biological evolution of the disease or are secondary to primary tumor heterogeneity. Certainly, repeating HER2 assessment during breast cancer trajectory is important for the increasing availability of effective anti-HER2 drugs. In response to this need, circulating biomarkers such as circulating tumor cells (CTCs) and cell-free circulating tumor DNA (ctDNA) offer the potential to safely and repeatedly assess HER2 status over time. This chapter outlines current methods for testing HER2 in CTCs and ctDNA, and reviews clinical trials evaluating its prognostic and predictive value in patients with breast cancer, as well as recent advances in the field.Copyright © 2023. Published by Elsevier Inc.