The metastatic spread of cancer is achieved by the haematogenous dissemination of circulating tumour cells (CTCs). Generally, however, the temporal dynamics that dictate the generation of metastasis-competent CTCs are largely uncharacterized, and it is often assumed that CTCs are constantly shed from growing tumours or are shed as a consequence of mechanical insults¹. Here we observe a striking and unexpected pattern of CTC generation dynamics in both patients with breast cancer and mouse models, highlighting that most spontaneous CTC intravasation events occur during sleep. Further, we demonstrate that rest-phase CTCs are highly prone to metastasize, whereas CTCs generated during the active phase are devoid of metastatic ability. Mechanistically, single-cell RNA sequencing analysis of CTCs reveals a marked upregulation of mitotic genes exclusively during the rest phase in both patients and mouse models, enabling metastasis proficiency. Systemically, we find that key circadian rhythm hormones such as melatonin, testosterone and glucocorticoids dictate CTC generation dynamics, and as a consequence, that insulin directly promotes tumour cell proliferation in vivo, yet in a time-dependent manner. Thus, the spontaneous generation of CTCs with a high proclivity to metastasize does not occur continuously, but it is concentrated within the rest phase of the affected individual, providing a new rationale for time-controlled interrogation and treatment of metastasis-prone cancers.

癌症的转移扩散是通过循环肿瘤细胞 (CTC) 的血源性传播来实现的。然而，一般来说，决定转移能力 CTC 生成的时间动态在很大程度上没有特征，并且通常认为 CTC 不断从生长的肿瘤中脱落或由于机械损伤而脱落¹. 在这里，我们观察到乳腺癌患者和小鼠模型中 CTC 生成动态的惊人和意外模式，强调大多数自发 CTC 血管内事件发生在睡眠期间。此外，我们证明静止期 CTC 非常容易转移，而在活动期产生的 CTC 缺乏转移能力。从机制上讲，CTC 的单细胞 RNA 测序分析显示，在患者和小鼠模型的休息阶段，有丝分裂基因显着上调，从而使转移能力得以提高。系统性地，我们发现褪黑激素、睾酮和糖皮质激素等关键的昼夜节律激素决定了 CTC 的生成动力学，因此，胰岛素直接促进体内肿瘤细胞增殖，但以时间依赖性方式。因此，