| Non-Hodgkin lymphoma (also called non-Hodgkin’s lymphoma, NHL, or just lymphoma) is cancer that starts in lymphoid tissue (also called lymph or lymphatic tissue). Other types of cancer (lung or colon cancers, for example) can start in other organs and then spread to lymphoid tissue. But these cancers are not lymphomas. Lymphomas start in the lymphoid tissue and can then spread to other organs.
There are 2 main types of lymphomas. Hodgkin lymphoma (also known as Hodgkin's lymphoma or Hodgkin disease) is named after Dr. Thomas Hodgkin, who described it as a new disease in 1832. All other types of lymphoma are called non-Hodgkin lymphomas. The cells of these 2 types of cancer look different under a microscope. But in some cases, special 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 (pronounced "limf") system.
Lymphoid tissue includes the lymph nodes and other organs that are part of the body's immune system, which makes some blood cells and protects against germs. The lymph system is mainly made up of lymphoid tissue (found in many places in the body), lymph vessels, and fluid called lymph (a clear fluid that contains waste products and excess fluid from tissues).
Lymphocytes
The main kind of cell found in lymphoid tissue is a type of white blood cell called the lymphocyte. There are 2 main types of lymphocytes: B cells and T cells. Most lymphomas (85%) start in the B cells. There are also many sub-types and stages of development of B and T cells. Normal T cells and B cells do different jobs within the immune system. Knowing the exact cell type of a lymphoma is the first step in deciding on a treatment.
Organs That Contain Lymphoid Tissue
Because lymphoid tissue is in many parts of the body, lymphomas can start almost anywhere. The major sites of lymphoid tissue are listed below.
Lymph nodes: These bean-sized organs are found throughout the body. They are made up mostly of lymphocytes and are connected by a system of vessels. These vessels are like veins except that instead of blood, they carry lymph fluid. Lymph fluid contains waste products and immune system cells.
Lymph nodes get bigger when they fight an infection. An enlarged or swollen lymph node is not usually a cause for concern. But a large lymph node is the most common sign of lymphoma.
Spleen: The spleen is found under the lower part of the rib cage, on the left side of the body. The spleen makes lymphocytes to help fight germs. It also stores healthy blood cells and filters out damaged blood cells, germs, and cell waste.
Thymus gland: The thymus gland lies just behind the breast bone and in front of the heart. The thymus plays a vital role in the development of T cells. It becomes smaller and less active as a person gets older but it continues to be an active part of the immune system.
Adenoids and tonsils: These are collections of lymph tissue found at the back of the throat. They fight germs that are breathed in or swallowed. They are easy to see if they become enlarged during an infection or if they become cancerous.
Digestive tract: The stomach and intestines, as well as many other organs, also contain some lymphatic tissue.
Bone marrow: The bone marrow (the soft inner part of bones) makes red blood cells, clotting cells (platelets), and white blood cells. Red blood cells carry oxygen from the lungs to the rest of the body. White blood cells fight infections. Platelets plug small holes in blood vessels caused by cuts or scrapes.
Types of Non-Hodgkin Lymphoma
Non-Hodgkin lymphomas are often divided into types based on how the cancer cells look under a microscope and their pattern of growth within the lymph node. There are about 30 different types of NHL. The classification system is very complex and can be confusing, even for many doctors.
Diffuse large B-cell lymphoma: This kind makes up about 1 out of 3 cases of lymphoma. The cells are large, and the cancer often grows quickly. It can affect any age group, but is mostly found in older people. About half of all people who have this kind of lymphoma are cured with treatment. Cure is most likely if the lymphoma was found in only 1 part of the body (localized).
Follicular lymphoma: About 1 out of 4 cases of lymphoma in the United States are of this type. The cells tend to grow in a circular pattern in the lymph nodes. This is a slow-growing cancer. It is found most often in older people and is rare in very young people. Although standard treatment will not often cure this cancer, people may live a long time with it. After 5 years, 60% to 70% of people with this type of cancer will still be alive. Over time, some follicular lymphomas change into the fast-growing diffuse B-cell type | 
