Normal Anatomy and the Development of Hodgkin Lymphoma

All blood cells start as stem cells in the bone marrow. Stem cells then mature into a variety of different blood cell types that have specific functions in the body. Hodgkin lymphoma is an abnormality with a type of white blood cells called lymphocytes. There are different types of lymphocytes, but the main types are:

• B-cell —Makes antibodies that help the body identify foreign substances in the body. The sooner the substance is identified the sooner the immune system can work on eliminating it.
• T-cell —T-cells have a number of jobs including destroying invading bacteria and viruses, or stimulating or slowing an immune response.

The lymphatic system is a network of fluid, vessels, organs, and lymph nodes throughout the body. The network carries fluids and immune cells. Lymphoid tissues and organs include:

• Lymph fluid —Clear fluid made up of plasma (a blood component that comes from general circulation), lymphocytes, cellular by-products, and proteins.
• Lymph vessels —Fluid from spaces between the cells and other bodily structures is collected by lymph capillaries (microscopic vessels) and moved into larger lymph vessels. Lymph is moved toward the heart by lymphatic and muscular contractions. The lymph is filtered through lymph nodes and eventually returned to the blood supply by draining into large veins near the collarbone.
• Lymph nodes —Lymphoid tissue that contains lymphocytes and other immune system cells. Lymph nodes are scattered throughout the body in clusters. Lymph vessels pass through lymph nodes. As lymph passes through, it is filtered for foreign bodies, including cancer cells. Lymph nodes can become swollen or painful when the body is fighting an infection.
• Bone marrow —All blood cells start as stem cells and are formed in bone marrow. Stem cells can mature into a variety of different blood cell types that have specific functions in the body.
• Spleen —Located under the rib cage on the left side of the body. The spleen helps the body fight infection by making lymphocytes and other immune system cells. It filters out cellular by-products from circulation. The spleen also removes and destroys old, damaged red blood cells.
• Thymus —Located behind the breastbone in the middle of the chest. The thymus makes T-cell lymphocytes where they stay until they are matured.
• Adenoids and tonsils —Located in the back of the throat. Tonsils make lymphocytes. They offer protection against foreign bodies that are inhaled or swallowed.

Lymphatic tissue can also be found throughout the body in the digestive tract, nervous system, and skin.

Lymphatic Tissue and Organs

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With Hodgkin lymphoma, there is an excessive development of B-cell lymphocytes. These cancerous cells are also abnormal and not able to carry out normal function of B-cells. The abnormal lymphocytes can also crowd out healthy cells in the lymph nodes, decreasing the number of effective cells and weakening the immune system. Cancerous blood cells also circulate in the blood and lymph systems and can gather in organs like the spleen, bone marrow, lungs, and liver.

Types of Lymphoma

There are 2 types of Hodgkin lymphoma based on their appearance under a microscope:

• Classic —Most common type of Hodgkin lymphoma. Abnormal cells, called Reed-Sternberg, are larger than normal B-cells. This type may appear in lymph nodes in any part of the body. There are 4 subtypes of Hodgkin lymphoma:
  • Nodular sclerosis (most common)—Tends to start in lymph nodes of chest and neck. Most common in teens and young adults.
  • Mixed cellularity—Most often starts in upper body. More common in older adults.
  • Lymphocyte-rich—Less common. Occurs in upper body.
  • Lymphocyte-depleted—Rare type. Mainly in older adults and often found in later stages with multiple organ and lymph involvement.
• Nodular lymphocyte predominant —Type of Reed-Sternberg cells that resembles popcorn when looked at under a microscope. This type most often starts in the lymph nodes in the neck or armpit.

In general, Hodgkin lymphoma is rare, but it is treatable and has a high cure rate.