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|Classification and external resources|
Follicular lymphoma replacing a lymph node
Lymphoma is a type of blood cancer that occurs when B or T lymphocytes, the white blood cells that form a part of the immune system and help protect the body from infection and disease, divide faster than normal cells or live longer than they are supposed to. Lymphoma may develop in the lymph nodes, spleen, bone marrow, blood or other organs and eventually they form a tumor.
Typically, lymphoma presents as a solid tumor of lymphoid cells. Treatment might involve chemotherapy and in some cases radiotherapy and/or bone marrow transplantation, and lymphomas can be curable depending on the histology, type, and stage of the disease. These malignant cells often originate in lymph nodes, presenting as an enlargement of the node (a tumor). It can also affect other organs in which case it is referred to as extranodal lymphoma. Extranodal sites include the skin, brain, bowels and bone. Lymphomas are closely related to lymphoid leukemias, which also originate in lymphocytes but typically involve only circulating blood and the bone marrow (where blood cells are generated in a process termed haematopoesis) and do not usually form static tumors. There are many types of lymphomas, and in turn, lymphomas are a part of the broad group of diseases called hematological neoplasms.
Signs and symptoms 
Lymphoma presents with certain non-specific symptoms. If symptoms are persistent, lymphoma needs to be excluded medically.
- Lymphadenopathy or swelling of lymph nodes - It is the primary presentation in lymphoma.
- B symptoms - Can be associated with both Hodgkin's lymphoma and non-Hodgkin's lymphoma. They consist of:
- Other Symptoms :
Lymphoma can be diagnosed by-
Immunophenotyping plays a major role in diagnosis. Histopathological findings of the various types of lymphoma are given in the table in the next section. A number of various classification systems exist for lymphoma. As an alternative to the American Lakes-Butler classification, in the early 1970s, Karl Lennert of Kiel, Germany, proposed a new system of classifying lymphomas based on cellular morphology and their relationship to cells of the normal peripheral lymphoid system.
Some forms of lymphoma are categorized as indolent (e.g. small lymphocytic lymphoma), compatible with a long life even without treatment, whereas other forms are aggressive (e.g. Burkitt's lymphoma), causing rapid deterioration and death. However, most of the aggressive lymphomas respond well to treatment and are curable. The prognosis therefore depends on the correct diagnosis and classification of the disease, which is established after examination of a biopsy by a pathologist (usually a hematopathologist).
Thomas Hodgkin published the first description of lymphoma in 1832, specifically of the form named after him, Hodgkin's lymphoma. Since then, many other forms of lymphoma have been described, grouped under several proposed classifications. The 1982 Working formulation became very popular. It introduced the category non-Hodgkin lymphoma, divided into 16 diseases. However, because these lymphomas have little in common with each other, the NHL label is of limited usefulness for doctors or patients and is slowly being abandoned. The latest classification by the WHO (2008) lists 70 forms of lymphoma divided into four broad groups.
Hodgkin’s disease has a bimodal distribution, occurring most commonly at ages 15–34 years and above 50 years. It is generally asymptomatic and presents with painless lymphadenopathy, usually in the cervical region. There are four main histological subtypes of Hodgkin’s: lymphocyte predominant, mixed cellularity, nodular sclerotic and lymphocyte depleted. Nodular sclerotic Hodgkin’s occurs most commonly in young adult patients. Staging of Hodgkin’s is based on the Ann Arbor classification, which is defined by lymph node involvement above and below the diaphragm and the presence of B symptoms (fever, night sweats or unexplained weight loss). Overall 10-year prognosis is good, but the presence of B symptoms is associated with adverse outcome.
Although older classifications referred to histiocytic lymphomas, these are recognized in newer classifications as of B, T or NK cell lineage. True histiocytic malignancies are rare and are classified as sarcomas.
Working formulation 
The 1996 Working Formulation is a classification of non-Hodgkin lymphoma. It excluded the Hodgkin lymphomas and divided the remaining lymphomas into four grades (Low, Intermediate, High, and Miscellaneous) related to prognosis, with some further subdivisions based on the size and shape of affected cells. This purely histological classification included no information about cell surface markers, or genetics, and it made no distinction between T-cell lymphomas or B-cell lymphomas.
It was widely accepted at the time of its publication but is now obsolete. It was superseded by subsequent classifications (see below) but it is still used by cancer agencies for compilation of lymphoma statistics and historical rate comparisons.
In the mid 1990s,the Revised European-American Lymphoma (REAL) Classification attempted to apply immunophenotypic and genetic features in identifying distinct clinicopathologic entities among all the lymphomas except Hodgkin's lymphoma. REAL has been superseded by the WHO classification. REAL & WHO •B-cell neoplasms –precursor –mature •T-cell neoplasms –precursor –mature •Hodgkin lymphoma •Non-HodgkinLymphomas
World Health Organization 
The WHO Classification, published in 2001 and updated in 2008, is the latest classification of lymphoma and is based upon the foundations laid within the "Revised European-American Lymphoma classification" (REAL). This system attempts to group lymphomas by cell type (i.e. the normal cell type that most resembles the tumor) and defining phenotypic, molecular or cytogeneticcharacteristics. There are three large groups: the B cell, T cell, and natural killer cell tumors. Other less common groups, are also recognized. Hodgkin lymphoma, although considered separately within the World Health Organization (and preceding) classifications, is now recognized as being a tumor of, albeit markedly abnormal, lymphocytes of mature B cell lineage.
Mature B cell neoplasms 
- Chronic lymphocytic leukemia/Small lymphocytic lymphoma
- B-cell prolymphocytic leukemia
- Lymphoplasmacytic lymphoma (such as Waldenström macroglobulinemia)
- Splenic marginal zone lymphoma
- Plasma cell neoplasms:
- Extranodal marginal zone B cell lymphoma, also called MALT lymphoma
- Nodal marginal zone B cell lymphoma (NMZL)
- Follicular lymphoma
- Mantle cell lymphoma
- Diffuse large B cell lymphoma
- Mediastinal (thymic) large B cell lymphoma
- Intravascular large B cell lymphoma
- Primary effusion lymphoma
- Burkitt lymphoma/leukemia
Mature T cell and natural killer (NK) cell neoplasms 
- T cell prolymphocytic leukemia
- T cell large granular lymphocytic leukemia
- Aggressive NK cell leukemia
- Adult T cell leukemia/lymphoma
- Extranodal NK/T cell lymphoma, nasal type
- Enteropathy-type T cell lymphoma
- Hepatosplenic T cell lymphoma
- Blastic NK cell lymphoma
- Mycosis fungoides / Sezary syndrome
- Primary cutaneous CD30-positive T cell lymphoproliferative disorders
- Primary cutaneous anaplastic large cell lymphoma
- Lymphomatoid papulosis
- Angioimmunoblastic T cell lymphoma
- Peripheral T cell lymphoma, unspecified
- Anaplastic large cell lymphoma
Hodgkin lymphoma 
- Classical Hodgkin lymphomas:
- Nodular sclerosis
- Mixed cellularity
- Lymphocyte depleted or not depleted
- Nodular lymphocyte-predominant Hodgkin lymphoma
Immunodeficiency-associated lymphoproliferative disorders 
- Associated with a primary immune disorder
- Associated with the Human Immunodeficiency Virus (HIV)
- Associated with methotrexate therapy
- Primary central nervous system lymphoma occurs most often in immuno-compromised patients, in particular those with AIDS, but it can occur in the immunocompetent as well. It has a poor prognosis, particularly in those with AIDS. Treatment can consist of corticosteroids, radiotherapy, and chemotherapy, often with methotrexate.
Other classification systems 
Following is a comparison of the most common types of lymphoma:
|Lymphoma type||Relative incidence||Histopathology||Immunophenotype||Overall
|Precursor T-cell leukemia/lymphoma||40% of lymphomas in childhood.||Lymphoblasts with irregular nuclear contours, condensed chromatin, small nucleoli and scant cytoplasm without granules.||TdT, CD2, CD7||It often presents as a mediastinal mass because of involvement of the thymus. It is highly associated with NOTCH1 mutations. Most common in adolescent males.|
|Follicular lymphoma||40% of lymphomas in adults||Small "cleaved" cells (centrocytes) mixed with large activated cells (centroblasts). Usually nodular ("follicular") growth pattern||CD10, surface Ig||72–77%||Occurs in older adults. Usually involves lymph nodes, bone marrow and spleen. Associated with t(14;18) translocation overexpressing Bcl-2. Indolent|
|Diffuse large B cell lymphoma||40 to 50% of lymphomas in adults||Variable. Most resemble B cells of large germinal centers. Diffuse growth pattern.||Variable expression of CD10 and surface Ig||60%||Occurs in all ages, but most commonly in older adults. Often occurs outside lymph nodes. Aggressive.|
|Mantle cell lymphoma||3 to 4% of lymphomas in adults||Lymphocytes of small to intermediate size growing in diffuse pattern||CD5||50% to 70%||Occurs mainly in adult males. Usually involves lymph nodes, bone marrow, spleen and GI tract. Associated with t(11;14) translocation overexpressing cyclin D1. Moderately aggressive.|
|B-cell chronic lymphocytic leukemia/lymphoma||3 to 4% of lymphomas in adults||Small resting lymphocytes mixed with variable number of large activated cells. Lymph nodes are diffusely effaced||CD5, surface immunoglobulin||50%.||Occurs in older adults. Usually involves lymph nodes, bone marrow and spleen. Most patients have peripheral blood involvement. Indolent.|
|MALT lymphoma||~5% of lymphomas in adults||Variable cell size and differentiation. 40% show plasma cell differentiation. Homing of B cells to epithelium creates lymphoepithelial lesions.||CD5, CD10, surface Ig||Frequently occurs outside lymph nodes. Very indolent. May be cured by local excision.|
|Burkitt's lymphoma||< 1% of lymphomas in the United States||Round lymphoid cells of intermediate size with several nucleoli. Starry-sky appearance by diffuse spread with interspersed apoptosis.||CD10, surface Ig||50%||Endemic in Africa, sporadic elsewhere. More common in immunocompromised and in children. Often visceral involvement. Highly aggressive.|
|Mycosis fungoides||Most common cutaneous lymphoid malignancy||Usually small lymphoid cells with convoluted nuclei that often infiltrate the epidermis, creating Pautier microabscesses.||CD4||75%||Localized or more generalized skin symptoms. Generally indolent. In a more aggressive variant, Sézary's disease, there is skin erythema and peripheral blood involvement.|
|Peripheral T-cell lymphoma-Not-Otherwise-Specified||Most common T cell lymphoma||Variable. Usually a mix small to large lymphoid cells with irregular nuclear contours.||CD3||Probably consists of several rare tumor types. It is often disseminated and generally aggressive.|
|Nodular sclerosis form of Hodgkin lymphoma||Most common type of Hodgkin's lymphoma||Reed-Sternberg cell variants and inflammation. usually broad sclerotic bands that consists of collagen.||CD15, CD30||Most common in young adults. It often arises in the mediastinum or cervical lymph nodes.|
|Mixed-cellularity subtype of Hodgkin lymphoma||Second most common form of Hodgkin's lymphoma||Many classic Reed-Sternberg cells and inflammation||CD15, CD30||Most common in men. More likely to be diagnosed at advanced stages than the nodular sclerosis form. Epstein-Barr virus involved in 70% of cases.|
Staging, prognosis, and treatment 
|This section requires expansion. (December 2012)|
|5-year relative survival by stage at diagnosis|
|Stage at diagnosis||5-year relative
of cases (%)
|Localized (confined to primary site)||82.1||28|
|Regional (spread to regional lymphnodes)||77.5||19|
|Distant (cancer has metastasized)||59.9||45|
These depend on the specific form of lymphoma. For some forms of lymphoma, watchful waiting is often the initial course of action. If a low-grade lymphoma is becoming symptomatic, radiotherapy or chemotherapy are the treatments of choice; although they do not cure the lymphoma, they can alleviate the symptoms, particularly painful lymphadenopathy. Patients with these types of lymphoma can live near-normal lifespans, but the disease is incurable. Treatment of some other, more aggressive, forms of lymphoma can result in a cure in the majority of cases, but the prognosis for patients with a poor response to therapy is worse. Treatment for these types of lymphoma typically consists of aggressive chemotherapy, including the CHOP or RCHOP regimen. Hodgkin lymphoma typically is treated with radiotherapy alone, as long as it is localized. Advanced Hodgkin disease requires systemic chemotherapy, sometimes combined with radiotherapy. See the articles on the corresponding form of lymphoma for further information.
Lymphoma is the most common form of hematological malignancy, or "blood cancer", in the developed world.
Taken together, lymphomas represent 5.3% of all cancers (excluding simple basal cell and squamous cell skin cancers) in the United States and 55.6% of all blood cancers.
According to the U.S. National Institutes of Health, lymphomas account for about five percent of all cases of cancer in the United States, and Hodgkin's lymphoma in particular accounts for less than one percent of all cases of cancer in the United States.
Because the whole system is part of the body's immune system, patients with a weakened immune system such as from HIV infection or from certain drugs or medication also have a higher incidence of lymphoma.
Research directions 
Significant research into the causes, prevalence, diagnosis, treatment, and prognosis of lymphoma is being performed. Hundreds of clinical trials are being planned or conducted at any given time. Studies may focus on effective means of treatment, better ways of treating the disease, improving the quality of life for patients, or appropriate care in remission or after cures.
In general, there are two types of lymphoma research: clinical or translational research and basic research. Clinical/translational research focuses on studying the disease in a defined and generally immediately patient-applicable way, such as testing a new drug in patients. By contrast, basic science research studies the disease process at a distance, such as seeing whether a suspected carcinogen can cause healthy cells to turn into lymphoma cells in the laboratory or how the DNA changes inside lymphoma cells as the disease progresses. The results from basic research studies are generally less immediately useful to patients with the disease.
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