Ki-67 promotes circulating tumor cell intravasation and metastasis in breast cancer

Hematogenous dissemination by circulating tumor cells (CTCs) drives metastatic spread. However, the molecular features that empower these cells to colonize distant organs remain unclear. We profiled single CTCs and CTC clusters from three breast cancer xenograft models by single-cell RNA sequencing and uncovered a shared transcriptional program marked by broad upregulation of cell-cycle genes. A targeted CRISPR loss-of-function screen identified MKI67 as an essential regulator of CTC abundance, particularly of cluster abundance, and metastatic progression. MKI67 disruption markedly reduced CTC numbers and decreased the fraction ofCTC clusters, leading to diminished lung metastases. CRISPRa-mediated re-expression of downstream adhesion genes CD47 and KLF4 restored both cluster prevalence and metastatic burden. Our findings link cell-cycle upregulation to enhanced metastatic capacity and position MKI67-dependent adhesion signals as tractable targpendent adhesion signals as tractable targets against metastatic spread.