Capillary bifurcations mechanically dissociate clusters of tumor cells

Circulating tumor cell (CTC) clusters are major drivers of cancer metastasis, possessing higher metastatic potential than equal numbers of single CTCs. While their ability to traverse linear capillary segments has been studied, their transit behaviors in capillary bifurcations remain poorly understood. We utilized live-cell imaging and microfluidic devices that replicate the diverse geometries of human capillary bifurcations to investigate the transit dynamics of breast cancer clusters. We demonstrate that clusters dissociate into smaller clusters and single cells and that this phenomenon is strongly influenced by geometric features of equal and small-sized daughter channels in capillary bifurcations. Moreover, inhibition of actin polymerization increases both the frequencies of cluster dissociation and cell lysis during cluster transit in capillary bifurcations. Overall, our findings suggest that capillary biomechanics and actin filament polymerization affect the integrity of CTC clusters.