How can lung cancer spread to the brain?

Lung cancer spreads to the brain through a process known as metastasis. This occurs when malignant cells detach from the primary lung tumor, invade surrounding tissues, and enter the circulatory system by penetrating the walls of blood vessels or lymphatic channels.1

Once in the bloodstream, these cancer cells are transported throughout the body. Eventually, they may lodge in the capillaries of distant organs, such as the brain. Upon exiting the vessels, the cells can multiply to establish secondary tumors.1

While the architecture of the circulatory system dictates that cells often travel "downstream" from their origin, the spread to specific sites like the brain is also influenced by "homing" mechanisms. This phenomenon may involve an affinity between receptor proteins on the surface of the cancer cells and specific molecules within the target tissue, or the presence of a favorable environment for tumor growth. Additionally, specific genetic defects within the cancer cells can facilitate this migration and colonization of distant tissues.1