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What is Hodgkin lymphoma?
Hodgkin lymphoma (HL) is a cancer that starts in lymphocytes. Lymphocytes are cells of the lymphatic system.
The lymphatic system works with other parts of your immune system to help your body fight infection and disease. The lymphatic system is made up of a network of lymph vessels, lymph nodes and the lymphatic organs. Lymph vessels carry lymph fluid, which contains lymphocytes and other white blood cells, antibodies and nutrients. Lymph nodes sit along the lymph vessels and filter lymph fluid. The lymphatic organs include the spleen, thymus, adenoids, tonsils and bone marrow.
Lymphocytes develop in the bone marrow from basic cells called stem cells. Stem cells develop into different types of cells that have different jobs. Lymphocytes are types of white blood cells that help fight infection. There are 2 types of lymphocytes:
- B cells stay in the bone marrow to mature.
- T cells move to the thymus to mature.
Lymphocytes sometimes change and no longer grow or behave normally. These abnormal cells can form tumours called lymphomas. Hodgkin lymphoma usually starts in abnormal B cells called Hodgkin and Reed-Sternberg cells, or HRS cells. These cells are much larger than normal lymphocytes and have a large nucleus or more than one nucleus.
Hodgkin lymphomas are divided into 2 main forms based on whether or not HRS cells are present:
- Classic HL means that the HRS cells are present. The classic forms of HL include nodular sclerosis HL, mixed cellularity HL, lymphocyte-rich classical HL and lymphocyte-depleted HL.
- Nodular lymphocyte predominant HL means there are very few or no HRS cells present.
Because lymphocytes are found throughout the lymphatic system, HL can start almost anywhere in the body. It usually starts in a group of lymph nodes in one part of the body, most often in the chest or neck or under the arms. It usually spreads in a predictable, orderly way from one group of lymph nodes to the next. Eventually, it can spread to almost any tissue or organ in the body through the lymphatic system or the bloodstream.
Other cancers of the lymphatic system are called non-Hodgkin lymphomas (NHL). The HRS cells of Hodgkin lymphoma look and behave differently from non-Hodgkin lymphoma cells. Hodgkin lymphomas and non-Hodgkin lymphomas are treated differently.