Hodgkin's disease is a cancer that originates in the nodes of the lymphatic system, the collection of organs, tissues, and vessels that produces infection-fighting cells and carries them throughout the body.
About 7,600 new cases of Hodgkin's disease (also called Hodgkin's lymphoma) are diagnosed in the United States earch year. Hodgkin's disease can occur throughout life but is most common in early adulthood (ages 15 to 40, peaking in people between 25 and 30). The majority of patients with Hodgkin's disease can have very good outcomes with current therapy.
The Lymphatic System
The organs and tissues that make up the lymphatic system include the lymph nodes, thymus, spleen, tonsils and adenoids, bone marrow, and lymphatic tissues in the gastrointestinal tract. Lymph (clear fluid from these tissues) contains proteins, immune cells, and waste products, and travels throughout the body in the vessels of this system. The lymph nodes (small bean-shaped organs found everywhere in the body but most notably in the neck, groin, underarms, and inside the pelvis, abdomen, and chest) produce and store white blood cells called lymphocytes, as do other lymphatic tissues. There are three kinds of lymphocytes: B lymphocytes (or B cells), T lymphocytes (or T cells), and natural killer (NK) cells. Each of these types of cells performs a unique job in the battle against infectious agents, targeting a very particular range of pathogens. They also play an important role in the body's fight against cancer.
How Hodgkin's Disease Arises
Hodgkin's disease arises when a lymphocyte (most often a B cell) undergoes a transformation from its normal state and becomes a malignant cell, one capable of uncontrolled growth and spread. The malignant cell begins producing identical copies of itself, or clones, in the lymph nodes. Over time these cells can spread to neighboring groups of lymph nodes, and if not treated, may spread to other parts of the body. In Hodgkin's disease, the tumors spread from lymph node group to lymph node group via the lymphatic vessels. The most common site of involvement is the lymph nodes in the chest; this region is called the mediastinum.
Physicians distinguish Hodgkin's disease from other types of lymphoma, in part, by examining tissue samples under a microscope; biopsied tissue from patients with Hodgkin's disease includes a certain number of cells called Reed-Sternberg cells (named after the two physicians who first described them). These distinctive cells are bigger than normal cells and have large, pale nuclei (the site in each cell where chromosomes -- genetic material -- are located).
Types of Hodgkin's Disease
The current system for classifying Hodgkin's disease is the WHO/REAL system (for World Health Organization/Revised European American Lymphoma classification). Using this system, physicians group lymphomas according to a number of characteristics: the appearance of the cells, their genetic features, their chemistry, and their clinical behavior. The WHO/REAL system describes two main types of Hodgkin's disease:
- Nodular lymphocyte-predominant Hodgkin's lymphoma, which accounts for 5 percent of cases of Hodgkin's disease.
- Classical Hodgkin's lymphoma, which accounts for 95 percent of cases.
In nodular lymphocyte-predominant Hodgkin's disease, which affects more men than women, the lymph nodes contain mostly reactive lymphocytes and malignant B cells called popcorn cells or lacunar cells.
Classical Hodgkin's disease is divided into three subtypes:
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Nodular sclerosis Hodgkin's lymphoma
In this form of the disease, which accounts for 70 to 80 percent of cases, the lymph nodes usually contain scar tissue (sclerosis), normal and reactive lymphocytes, and Reed-Sternberg cells.
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Mixed cellularity Hodgkin's lymphoma
In this form of the disease, which accounts for 20 percent of cases, the lymph nodes contain Reed-Sternberg and inflammatory cells, and sclerosis is absent.
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Lymphocyte depletion Hodgkin's lymphoma
There are two types of this form of the disease, one with layers of malignant cells, the other with few Reed-Sternberg cells and lymphocytes. In recent years, the incidence of this form has declined for reasons that are not clear.
Classical and nodular lymphocyte-predominant Hodgkin's disease each have particular genetic and clinical features that distinguish them from each other.
