  Distant spreading of primary lesions is modulated by the vascular dynamics of
circulating tumor cells (CTCs) and their ability to establish metastatic
niches. While the mechanisms regulating CTC homing in specific tissues are yet
to be elucidated, it is well documented that CTCs possess different size,
biological properties and deformability. A computational model is presented to
predict the vascular transport and adhesion of CTCs in whole blood. A
Lattice-Boltzmann method, which is employed to solve the Navier-Stokes equation
for the plasma flow, is coupled with an Immersed Boundary Method. The vascular
dynamics of a CTC is assessed in large and small microcapillaries. The CTC
shear modulus k ctc is varied returning CTCs that are stiffer, softer and
equally deformable as compared to RBCs. In large microcapillaries, soft CTCs
behave similarly to RBCs and move away from the vessel walls; whereas rigid
CTCs are pushed laterally by the fast moving RBCs and interact with the vessel
walls. Three adhesion behaviors are observed, firm adhesion, rolling and
crawling over the vessel walls, depending on the CTC stiffness. On the
contrary, in small microcapillaries, rigid CTCs are pushed downstream by a
compact train of RBCs and cannot establish any firm interaction with the vessel
walls; whereas soft CTCs are squeezed between the vessel wall and the RBC train
and rapidly establish firm adhesion. These findings document the relevance of
cell deformability in CTC vascular adhesion and provide insights on the
mechanisms regulating metastasis formation in different vascular districts.
