Liquid biopsy has been introduced as a new diagnostic concept predicated on the analysis of circulating tumour cells (CTCs) or circulating tumour-derived factors, in particular, cell-free tumour DNA (ctDNA). Highly sensitive liquid biopsy assays have been developed that can now be applied to detect and characterize minimal residual disease (MRD), which reflects the presence of tumour cells disseminated from the primary lesion to distant organs in patients who lack any clinical or radiological signs of metastasis or residual tumour cells left behind after local therapy that eventually lead to local recurrence. This application is the new frontier of liquid biopsy analyses, which are challenged by the very low concentrations of CTCs and ctDNA in blood samples. In this Review, we discuss the key technologies that can be used to detect and characterize CTCs in surveillance of MRD and provide a brief overview of similar roles of ctDNA analyses. We then focus on the current clinical data on the use of CTCs and ctDNA in the detection and monitoring of MRD and in obtaining information on therapeutic targets and resistance mechanisms relevant to the management of individual patients with cancer.

液体活检已被引入作为一种新的诊断概念，其依据是对循环肿瘤细胞（CTC）或循环肿瘤衍生因子，特别是无细胞肿瘤DNA（ctDNA）的分析。已开发出高度灵敏的液体活检测定法，现在可将其用于检测和表征最小残留疾病（MRD），这反映了缺乏任何临床或放射学转移迹象的患者中从原发灶扩散到远处器官的肿瘤细胞的存在或局部治疗后残留的残留肿瘤细胞最终导致局部复发。这项应用是液体活检分析的新领域，因为血液样本中的CTC和ctDNA浓度非常低，因此面临挑战。在这篇评论中，我们讨论了可用于检测和表征MRD监测中CTC的关键技术，并简要概述了ctDNA分析的相似作用。然后，我们将重点放在有关使用CTC和ctDNA来检测和监测MRD以及获得与个体癌症治疗相关的治疗靶点和耐药机制的信息方面的当前临床数据。