Hodgkin Lymphoma Clinical Resource Area - Disease Overview

Normal Anatomy and Physiology
The lymphatic system is a complex network which consists of lymphoid organs, lymph nodes, lymph ducts, lymph tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. The lymphatic system acts as a secondary circulatory system, except that it collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria.

Humans have approximately 500-600 lymph nodes distributed throughout the body, with clusters found in the axilla, groin, neck, chest, and abdomen. Human lymph nodes are bean-shaped and range in size from a few millimeters to about 1-2 cm in their normal state. They act as filters that collect and destroy bacteria and viruses. White blood cells (lymphocytes) are located within the lymph nodes. Both T lymphocytes and B lymphocytes constantly circulate through the lymph nodes. When the body is fighting an infection or if tumor cells (HL cells) are present, lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes.

The thymus, spleen, lymph nodes, peyer's patches, tonsils, vermiform appendix, and red bone marrow are considered to be accessory lymphoid tissues that comprise the lymphoid organs. These organs contain circulating B-and T-lymphocytes and other immune cells like macrophages and dendritic cells. These lymphoid organs may be affected when a person has HL.

Epidemiology
Unlike other lymphomas, whose incidence increases with age, Hodgkin lymphoma has a bimodal incidence curve; that is, it occurs most frequently in two separate age groups, the first being young adulthood (age 15–35) and the second being in those over 60 years old. Overall, it is more common in men, except for the nodular sclerosis variant which is more common in women.

The annual incidence of Hodgkin lymphoma is about 1/25,000 people, and the disease accounts for slightly less than 1% of all cancers worldwide.

Risk Factors
Although most cases of Hodgkin lymphoma occur in people who do not have identifiable risk factors, t he following are some of the risk factors associated with this disease:

• Age/Sex - Hodgkin lymphoma occurs most often in people between 15 and 34 and in people over the age of 55. It is more common in men than in women.
• Family History - Brothers and sisters of those with Hodgkin lymphoma have a higher-than-average chance of developing this disease.
• Viruses - Epstein-Barr virus is an infectious agent that may be associated with an increased chance of getting HL, however, its precise role in the predisposition or onset of this disease is still under study. In addition, Hodgkin lymphoma occurs with greater frequency among persons infected with the human immunodeficiency virus (HIV), although the virus itself is not considered to be the direct cause of Hodgkin lymphoma.

Prevention and Screening
The overwhelming majority of cases of Hodgkin lymphoma cannot be prevented since we do not know the cause. Scientists have been working on vaccine strategies against Epstein-Barr virus associated diseases. This work has been hampered by an inability to identify the characteristics of the virus when it remains dormant in the body. However, there is currently some optimism that vaccine trials aimed at controlling infectious mononucleosis, post-transplant lymphoproliferative disease, nasopharyngeal carcinoma and Hodgkin lymphoma may be performed in the future.

In order for screening to be effective, patients at risk for Hodgkin lymphoma need to be identifiable. This is not currently possible, with the exception of identifying patients who have one of a few genetic diseases and screening them accordingly.