Types of Lymphoma
There are two primary types of lymphoma: Hodgkin lymphoma (HL, also called Hodgkin's disease), which is characterized by the presence of large distinctive cells called Reed-Sternberg cells, and non-Hodgkin lymphoma (NHL), a large group of other lymphomas.
Hodgkin lymphoma is most prevalent in two age groups: in those between about 20 and 40 years of age and in those over 55. According to the American Cancer Society (ACS), about 9,000 people in the United States are diagnosed with Hodgkin lymphoma each year and about 1,300 people die of it.
There are many different theories concerning the cause of HL. Some think that a type of infectious agent, such as a virus, might be involved. Others think that a mutation in a cell is the cause. While this is an area of active research, specific causes have not yet been identified. Likewise, there is no clear understanding of why males seem to be slightly more susceptible to the disease.
HL can be subdivided based on the structure of the abnormal lymph node and the types of cells that are present. Lymph nodes may have a predominance of small lymphocytes, the presence of bands of scarring (fibrosis), a mixture of different cell types, or lymphocyte depletion. In HL, tumor cells (so-called Reed-Sternberg cells) are the minority, while the majority is a benign, often mixed, reactive cell population.
Non-Hodgkin lymphoma represents just over 4% of all new cancer cases in the United States. It is slightly more common in men than women and more common in Caucasians. The incidence of NHL increases with age and is higher in those with HIV/AIDS and in people whose immune system is suppressed.
According to the ACS, non-Hodgkin lymphoma accounts for about 4% of all cancers. About 72,000 people are diagnosed with non-Hodgkin lymphoma per year and about 20,000 people die from it. Incidence rates of NHL have almost doubled since the 1970s. The reasons for this are not yet known, but the greatest increase has been in women. However, death rates from non-Hodgkin lymphoma have been decreasing since the late 1990s.
There are many types of non-Hodgkin lymphoma and as knowledge about them grows, the systems used to classify them has evolved. New methods of evaluating the cells involved in non-Hodgkin lymphoma have led to changes in classification systems.
In the 1990s, the Revised European American Lymphoma (REAL) classification was proposed by the International Lymphoma Study Group and adopted by many physicians. It looked at the function that the cell should be providing. B-lymphocytes are responsible for producing antibodies, for instance, while T-lymphocytes are responsible for cell-to-cell interactions. The newest method, the World Health Organization or WHO Classification, combines these characteristics with phenotypic and genetic studies of the cells. The WHO classification expanded on REAL and has been accepted by many as the current standard.
Some Types of Non-Hodgkin Lymphomas
Classification of non-Hodgkin lymphomas can be confusing because there are so many different types and because of the various classification systems that have been developed and amended over the years. In the United States, B-cell non-Hodgkin lymphomas are much more common than T-cell and NK-cell lymphomas. About 85% of non-Hodgkin lymphomas involve mature B-lymphocytes with about 15% affecting T-lymphocytes.
Some of the more common forms of B-cell lymphomas include:
- Diffuse large B-cell lymphoma (DLBCL): this form constitutes about one in three cases of all non-Hodgkin lymphomas in the United States. It is a fast-growing lymphoma and can affect anyone of any age but occurs mostly in older people.
- Follicular lymphomas: these make up about one in five of all lymphomas in the U.S. This is generally a very slow-growing lymphoma, but over time about one in three turns into a fast-growing DLBCL.
- B cell chronic lymphocytic leukemia / small lymphocytic lymphoma (CLL / SLL): this is a slow-progressing disease in which the lymphoma cells are predominantly small in size. CLL / SLL is the same disease; however, CLL mainly involves the bone marrow and the blood while SLL is found mainly in the lymph nodes. These two together make up approximately 24% of all lymphomas.
Some of the more common forms of T-cell lymphomas include:
- Precursor T-lymphoblastic lymphoma (leukemia): a disease that can be considered either a lymphoma or leukemia depending on whether affected cells are found in the blood and/or in the bone marrow. About 1% of all lymphomas are this type.
- Mature or peripheral T-cell lymphomas: there are many different kinds of mature T-cell lymphomas that all together make up about 4% to 5% of all lymphomas.
- Cutaneous T-cell lymphomas (mycosis fungoides, Sezary syndrome, and others): these are less common forms of lymphoma but are unusual because, while most lymphomas begin in lymphoid tissue or internal organs, these types start in the skin. This group of skin cancers makes up less than 1% of nonmelanoma skin cancers. Skin lymphomas make up 5% of all lymphomas.