Lymph nodes are small, bean-shaped organs that are part of the lymphatic system and are located throughout the body, including the neck, armpit, chest, abdomen, and groin. They work as filters for foreign substances, such as cancer cells and infections, and contain immune cells that can help fight infection by attacking and destroying germs that are carried in through the lymph fluid. Lymph fluid flows through the tissue that makes up lymph nodes, where the tissue filters and recycles lymph fluid that the body needs. The cells within lymph nodes attack, destroy, and eliminate waste, especially foreign invaders, to help the immune system keep the body healthy. Lymph nodes play an important role in cancer, including its diagnosis and treatment, as cancer can start in lymph nodes (such as in lymphoma), and some other types of cancer can also spread from one part of the body to another through lymph nodes.