These facts about lymphoma explain what type of blood cell cancer it is and include terminology that haematologists use when diagnosing lymphoma and discussing treatment options.
Lymphoma is a type of blood cancer that comes from the lymphoid tissue. The main cells of lymphoid tissue are lymphocytes. These are part of our immune system and play a very important role in protecting our body against infection and other diseases. Lymphocytes are present in blood and in lymphoid tissue throughout the human body. When lymphocyte development becomes abnormal, people may develop lymphoma. The main lymphoid tissue is present in lymph nodes (lymph glands), spleen, and bone marrow. Lymphoma usually develops in these sites, although it may affect any human organ.
There are many lymphocyte subtypes, with different functions and each one may give rise to a different type of lymphoma. The main subtypes of lymphocytes are B cells and T cells, both of which themselves have many subtypes. Most B cells are involved in production of antibodies, whilst T cells are involved both in direct destruction of infections and in the regulation of protection against infections. B cell lymphomas are more common (90%) than T cell lymphomas.
Each lymphoma subtype has its own natural course. Presenting symptoms, response to treatment and prognosis vary significantly among the different lymphoma subtypes.
The exact cause of lymphoma is not known, but there are risk factors that may increase a person’s likelihood of developing lymphoma. Exposure to certain chemicals, including benzene, some pesticides, cigarettes and chemotherapy drugs used for cancer treatment increase the risk of developing lymphoma. Radiation including radiotherapy also increases the risk for lymphoma. Certain diseases of the immune system, including illnesses that impair the body’s ability to fight infection predispose to lymphoma. Also, certain infections may make people more susceptible. Viruses such as Epstein-Barr virus, HIV or Human T-lymphotropic virus (HTLV) increase the risk for lymphoma.
Lymphoma often develops in lymph nodes: the lymph nodes swell and patients may notice lumps in the neck, underarms, groins or elsewhere. Sometimes patients develop fever, drenching night sweats and weight loss. There may also be loss of appetite and fatigue. All these together are called B symptoms. They are not specific for lymphoma. These symptoms may be seen in many other diseases, including infections and other cancers, so diagnosing lymphoma is not always straightforward. To reach a diagnosis, it is necessary to perform a biopsy of the affected lymph nodes or other affected lymphoid tissue. The biopsy result not only confirms the diagnosis, but also establishes the exact type of lymphoma. Sometimes, special genetic tests may also be required to reach an accurate diagnosis. This is very important, as lymphoma is not really a single type of cancer but rather a large group of distinct entities.
The stage measures how widely has a lymphoma spread around the body. The Ann-Arbor staging system is the most commonly used and has four stages. Stages I and II are referred to as early stage and III and IV are considered advanced stages.
In addition to this the system uses the letter A for patients without significant night sweats, significant weight loss or lymphoma-associated fever, and the letter B for patient with these symptoms. The letter S is used for lymphoma that has spread to the spleen and the letter E if it has spread outside lymph nodes or spleen.
There are two main types of lymphoma: Hodgkin lymphoma and Non-Hodgkin lymphoma. Each of these main types has many subtypes. All these can be distinguished by examining the biopsy sample.
Hodgkin lymphoma was named after Dr Thomas Hodgkin who described it in 1832. There are two major subtypes: Classical Hodgkin lymphoma, which is characterised by the presence of large cells called Hodgkin and Reed-Stenberg cells. These are abnormal cancer cells that are surrounded by inflammatory tissue. According to the appearance of this surrounding inflammatory tissue, different subtypes of classical Hodgkin lymphoma can be recognised. The rarer subtype of Hodgkin lymphoma is called nodular lymphocyte predominant Hodgkin lymphoma and this has slightly differently looking malignant cells called variant Reed-Stenberg cells or popcorn cells.
The treatment of Hodgkin lymphoma is very successful. Most patients, particularly those with early stage disease will be cured with chemotherapy alone or in combination with radiotherapy. A few patients may fail treatment or experience lymphoma relapses after the initial treatment. Many of these patients will be cured with further chemotherapy and a stem cell transplant.
The majority of patients with lymphoma are diagnosed with non-Hodgkin lymphoma. Like Hodgkin lymphoma this is not a single disease but a large group of very different cancers. Some of them are slow growing, indolent and may not even require any treatment. Other types can be very aggressive, fast growing and make patients unwell rapidly. Some types are well known to respond favourably to treatment and some are not. The subtypes are characterised by their appearance under the microscope, the pattern of proteins within the membranes of lymphoma cells and by changes in different genes. New types of rare lymphoma are still being described.
Most non-Hodgkin lymphomas are related to lymphocytes called B cells and are therefore called B cell lymphomas. Some lymphomas are related to T cells and rarely lymphomas can be related to other types of lymphocytes.
Common B cell lymphomas are:
The most common T-cell lymphomas are: