When a tumor reaches a large size, a mechanism called metastasis is used to invade foreign tissue. This happens when the tumor sends a cell into a blood vessel into the blood, where it expresses various proteins like flagella(to aid the movement of the cell), CXCR4(C-X-C receptor 4, which regulates migration signal), and various adhesion proteins such as integrin beta, when the target site is reached. Once CXCR4 binds to a migration signal(chemokine) known as SDF1, the invasive cancer cell expresses beta-2 integrin on its surface, allowing it to bind to adhesion proteins such as ICAM-1. This ultimately leads to intravasion(the invading of tissue by squeezing out of the bloodstream).
Normally, chemokines are secreted by Antigen presenting immune cells in order to guide T and B cells to the site of infection. Instead. cancer cells follow these signal to find and invade new tissue.
