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Non-Hodgkin Lymphoma
Introduction
Non-Hodgkin lymphoma (also known as non-Hodgkin's lymphoma, NHL, or sometimes just lymphoma) is a cancer
that starts in cells of the lymph system, which is part of the body's
immune system. Lymph cells (called lymphocytes)
are located mainly in the lymph nodes and other lymphoid tissues (such as the spleen or bone marrow). These will
be described in more detail in the section The Lymph System and Lymphoid Tissue.
Other types of cancer -- lung or
colon cancers, for example -- can spread to lymph tissue such as the lymph nodes or bone marrow. But cancers
that start in these places and then spread to the lymph tissue are not lymphomas.
Types of Lymphoma
There are 2 main types of lymphomas. Hodgkin lymphoma (also known as Hodgkin's lymphoma, Hodgkin disease,
or Hodgkin's disease) is named after Dr. Thomas Hodgkin, who first described it. Hodgkin disease is discussed
in a separate American Cancer Society document. All other types of lymphoma are called non-Hodgkin lymphomas.
These 2 types of lymphoma can usually be distinguished from each other by looking at the cancer cells under
a microscope. In some cases, sensitive lab tests may be needed to tell them apart.
The Lymph System and Lymphoid Tissue
To understand what lymphoma is, it helps to know about the body's lymph system.
The lymph system (also known as the lymphatic system) is composed mainly of lymphoid tissue, lymph vessels,
and fluid called lymph (a clear fluid containing waste products and excess fluid from tissues). Lymphoid
tissue is formed by several types of immune system cells that work together to help the body fight infections
. Lymphoid tissue is found in many places throughout the body (described below).
Lymphocytes
Most of the cells found in lymphoid tissue are lymphocytes, a type of white blood cell. The 2 main types of
lymphocytes are B lymphocytes (B cells) and T lymphocytes (T cells). Both types can develop into lymphoma
cells, but B-cell lymphomas are much more common than T-cell lymphomas in the United States.
Normal T cells and B cells do different jobs within the immune system.
By producing proteins known as antibodies, B cells often assist the body in defending itself against pathogens
(bacteria or viruses). attach to the bacteria or viruses and attract other immune system cells that surround and
digest the antibody-coated germs. Antibodies also attract certain blood proteins that can kill bacteria.
There are several types of T cells, each with a specialized job. Some normal T cells help protect the body
against viruses, fungi, and some bacteria.They kill virus-infected cells by identifying certain chemicals
present in those cells. Additionally, T cells have the capacity to secrete cytokines, which draw specific
other subtypes of white blood cells and cause them to ingest the infected cells. T cells are also believed
to kill some cancerous cells and the cells from transplanted organs. Certain T cell subtypes can either
stimulate or inhibit the activity of other immune system cells.
Lab tests identify B cells and T cells by certain substances on their surfaces. Some substances are found only
on B cells, and others are found only on T cells. There are also several stages of B-cell and T-cell development
(or maturation) that can be recognized by these lab tests.
This information is helpful because each type of lymphoma tends to resemble a particular subtype of normal
lymphocytes at a certain level of development. Determining the type of lymphoma a person has is the first
step in considering treatment options.