Memorial Sloan Kettering experts discuss lymphoma, a type of cancer that arises in white blood cells called lymphocytes.
Each year, approximately 75,000 people in the United States are diagnosed with lymphomas, one of the most common forms of cancer.
Lymphomas begin in white blood cells called lymphocytes — immune-system cells that help the body fight infection and diseases such as cancer. Lymphomas occur when the genetic material within a lymphocyte becomes defective, either at random or due to age or the presence of certain types of infections. Only in very rare cases is the risk for lymphomas inherited.
Lymphoma cells can also receive abnormal and sustained growth signals from cells in the surrounding area (known as the microenvironment), causing the lymphoma cells to grow abnormally and form tumors.
Types of Lymphomas
Lymphomas are a diverse group of more than 60 related cancers. Doctors identify each by the type of lymphocyte in which the cancer began, such as B cells, T cells, and NK cells. Lymphocytes are found in organs and tissues of the lymphatic system, including the lymph nodes, bone marrow, thymus, spleen, tonsils, and lymphoid tissue in the digestive tract.
About nine in ten lymphomas develop in the body’s B cells, which are produced in the bone marrow.
Lymphomas are divided into two broad categories:
- Non-Hodgkin lymphomas are the most common type. While they can occur at any age, most people who develop the illness are older. Of the dozens of types identified to date, just 13 account for nearly 90 percent of all non-Hodgkin lymphomas in the United States. These include diffuse large B cell lymphoma, primary mediastinal B cell lymphoma, follicular lymphoma, small lymphocytic lymphoma, mantle cell lymphoma, and Burkitt lymphoma. There are also several types of T cell lymphoma, but these are relatively rare. Non-Hodgkin lymphomas are often classified as aggressive (fast growing) or indolent (slow growing and often referred to as “low grade”).
- Hodgkin lymphomas usually begin in a type of B cell called a Reed-Sternberg cell, named after the two doctors who first identified it. Approximately 95 percent of Hodgkin lymphomas are considered classic Hodgkin lymphoma, a type that is further subtyped, based on its appearance in the body and under the microscope, into the following categories: nodular sclerosis Hodgkin lymphoma, mixed cellularity Hodgkin lymphoma, lymphocyte-rich Hodgkin disease, and lymphocyte-depleted Hodgkin disease. The other major type of Hodgkin lymphoma, nodular lymphocyte-predominant Hodgkin disease is very rare.
Most people with lymphomas have no identifiable risk factors.
Although rare, the primary risk factor that has been recognized to date is having a weakened immune system due to such causes as an inherited disorder, HIV infection, or the use of medicines to prevent rejection of a transplanted organ.
In addition, infections such as human T cell leukemia/lymphotropic virus (HTLV-1) or Helicobacter pylori can increase the risk of lymphomas. Exposure to certain pesticides, solvents, fertilizers such as nitrates, and herbicides may increase the risk for non-Hodgkin lymphomas.
Swollen or enlarged lymph nodes are most often a normal sign of a viral or bacterial infection and are not related to cancer. However, when lymph nodes remain swollen long after an infection has resolved or appear unrelated to an infection, doctors may consider lymphomas as a possible cause.
Lymphomas can begin in lymph nodes almost anywhere in the body, as well as in the bone marrow and thymus. Symptoms usually arise in the area affected:
- Lymphomas that develop in lymph nodes under the skin in the neck, underarms, or groin may cause ongoing painless swelling.
- Lymphomas in the stomach or intestines can cause bleeding, a feeling of persistent fullness, or abdominal swelling.
- Lymphomas in the brain and spinal cord can cause neurological symptoms such as partial paralysis, seizures, confusion, and trouble walking.
- Lymphomas in the chest can cause coughing, shortness of breath, and pain.
Other symptoms of lymphomas may include fever, fatigue, night sweats, unexpected weight loss, and itching. Some people with Hodgkin lymphomas experience pain when drinking alcohol. Because most of these symptoms can be caused by a variety of conditions, it’s important to see a doctor if they persist to determine the cause.