The tumor-infiltrating immune cells recognize non-self antigens derived from tumor cells. Those antigens are bound to antibodies secreted mainly in the blood, which is why angiogenesis is relatively and positively related to the efficiency of the immune cells's infiltration. It is widely accepted that the tumors in the Lynch syndrome (DNA mismatach repair syndrome) have a lot of immune cells in the stroma.
Tumor-induced vessels, e.g HEV-like vessels, are important for tumor-infiltrating immune cell migration. These vessels express chemokines and cytokines are also very helpful for the immune cells distribution.
Many cell migrate to the tumor site due attraction towards CC release by tumor cells. and some infiltration of immune facilitate migration of APCs. it is easy for immune cells.