Figure 4.

Base case: more details of the cell migration which takes place between primary tumor periphery and the lymphatic placed in the upper-left corner are shown. (a) The total cell velocity ${\mathbf{u}}_{\text{c}}$ shows that in the peritumoral region there is a dominating downstream cell migration toward the lymphatic whereas close to the rim, tumor cells are guided back to the primary tumor which will keep it densely packed. (b) Dispersive cell velocity does not contribute outside the primary tumor. (c) Associated with the finger-like clusters of tumor cells there is a weak upstream migration that ensures that the cell volume fraction is kept low by driving tumor cells back to the primary tumor. The upstream migration represented by ${\mathbf{u}}_{c,\text{fluid}-\text{stress}}$ is weak in this region (since the cell volume fraction ${\alpha }_{\text{c}}$ is very low) but has a dominating effect close to the tumor periphery where the cell volume fraction increases rapidly. (d) The chemotactic vell velocity component ${\mathbf{u}}_{c,\text{chemotaxis}}$ drives the downstream migration.