The lymphatic system is the circulation system for lymph. Just like blood vessels carry blood throughout the body, the lymphatic system carries lymph throughout the body. The lymphatics are a network of tubes that carry the clear fluid called lymph. The lymph carries white blood cells, which makes the lymphatic system a critical part of the immune system. Lymph nodes or glands are part of the lymphatic system, as well. These little glands filter viruses, bacteria and other invaders as they pass by in the lymph. They quarantine these invaders in the lymph gland and hold them there until the white blood cells can destroy and dispose of them. Because lymph moves around the body in this circulatory system, any cancer that arises in the lymph (for example, lymphoma) is by definition systemic, meaning “it’s everywhere.” Other types of cancer can use the lymphatics to metastasize or spread, too. That’s why your oncologist might want to aspirate or even biopsy lymph nodes as part of staging cancer.