Lymphoma refers to a family of cancers in the lymphatic system. It accounts for about 3% of cancers. The lymphatic system includes the organs, tissues, and vessels in the immune system responsible for fighting disease and infection throughout the body. Lymphoma affects the blood and the lymphatic system - that includes lymph nodes (like the ones in your neck that get swollen when you have a bad cold), the spleen, bone marrow, and an immune gland in the chest called the thymus.