Lymphoma is a cancer of the lymphatic system. The lymphatic system is part of your immune system, which helps protect you from infection. It is spread throughout your body, like blood vessels, and has many different parts. This factsheet describes the different parts of the lymphatic system and what they do: What is the lymphatic system?; Lymph; Lymph nodes; Bone marrow; Thymus; Spleen; Tonsils and adenoid; Mucosa-associated lymphoid tissue; The lymphatic system and lymphoma.