Primary central nervous system (CNS) lymphoma is a disease in which malignant cells form in the lymph tissue of the brain and/or spinal cord. Lymphoma is a disease in which cancer develops in the lymph system, which is part of the immune system, and is made up of the lymph, lymph vessels, lymph nodes, spleen, thymus, tonsils, and bone marrow.
Lymphocytes (carried in the lymph) travel in and out of the CNS. It is thought that some of these lymphocytes become malignant and cause lymphoma to form in the CNS.
Having a weakened immune system may increase the risk of developing primary CNS lymphoma.Primary CNS Lymphoma Treatment (PDQ®)
Source: National Cancer Institute