Estimated new cases and deaths from non-Hodgkin's lymphoma (NHL) in the United States in 2005:
- New cases: 56,390.
- Deaths: 19,200.
In the United States, the incidence has increased from 6.9 per 100,000 population in 1947 to 1950 to 17.4 per 100,000 population in 1984 to 1988.
Male : female ratio is about 1.5:1.
Except for high-grade lymphoblastic and Burkitt lymphomas (the most common types of NHL seen in children and young adults), the median age at presentation for all subtypes of NHL exceeds 50+ years. Low-grade lymphomas account for 37% of NHLs in patients between the ages of 35 and 64 years at diagnosis but for only 16% of cases in those younger than age 35.
Race and ethnicity
Incidence varies by race, with whites at higher risk than blacks and Asian-Americans. Most histologies, particularly low-grade small lymphocytic and follicular lymphomas, are more common in whites than blacks. The incidence of mycosis fungoides and other peripheral T-cell lymphomas is higher in black males and lowest in white females.
Certain endemic geographic factors appear to influence the development of NHL in specific areas:
- Burkitt lymphoma in Africa
- Immunoproliferative small intestinal disease (?-chain disease) is rarely encountered in individuals other than those of Mediterranean ethnic origin.
- Human T-cell lymphotrophic virus-1 (HTLV-1) associated T-cell lymphoma/leukemia occurs more frequently in Japan (Kyushu) and the Caribbean.
- Peripheral T-cell lymphomas are more common in Europe and China than in North America.
- Follicular lymphomas are more common in North America and Europe but are rare in the Caribbean, Africa, China, Japan, and the Middle East.
Causes and risk factors
In order to remember the chromosomal abnormalities involved in the pathogenesis of NHL we must first understand the key genes involved in the various NHL subtypes and their corresponding chromosome number.
Since the primary function of lymphocytes is the formation of antibodies, a common set of genes affected in NHL are those responsible for the formation of the heavy and light chains of the antibody. These genes are found on the following chromosomes:
- Heavy chain: chromosome 14.
- Light chain kappa: chromosome 2.
- Light chain lambda: chromosome 22.
Besides the above set of genes there are key genes that are specific to each particular subset of NHL.
- The main gene (in up to 90% of cases) affected is the bcl-2 gene located on chromosome 18.
- Hence, follicular lymphoma is characterized by a translocation involving both the bcl-2 gene and the heavy chain gene that is: t(14;18).
Small noncleaved NHL and Burkitt lymphoma
The main gene involved is the c-myc gene located on chromosome 8.
Translocations in Burkitt's lymphoma will involve c-myc and all the 'antibody genes': t(8;14), t(2;8), t(8;22).
Large cell lymphoma
- The main gene involved is bcl-6 located on chromosome 3.
- Translocations found in large cell NHL are: t(3;14), t(2;3) and t(3;22)
Small lymphocytic type
- The main gene involved is bcl-3 located on chromosome 19.
- The translocation found in small lymphocytic lymphoma is t(14;19).
Mantle cell lymphoma
- The main gene involved is bcl-1 located on chromosome 11.
- The translocation found in mantle cell lymphoma is t(11;14).
The translocation found in plasmacytoid lymphoma is t(9;14).
Lymphoblastic T-cell lymphoma
- Variable involvement of T-cell receptor genes.
Anaplastic large cell lymphoma
- This results from the fusion of the nucleophosmin gene (NPM) to a tyrosine kinase ALK (anaplastic lymphoma kinase): t(2;5).
Certain workers have a slightly increased risk of developing NHL, including farmers; pesticide applicators; grain (flour) millers; meat workers; wood and forestry workers; chemists; painters; mechanics; machinists; printers; and workers in the petroleum, rubber, plastics, and synthetics industries.
Chemicals that have been linked to the development of NHL include a variety of pesticides and herbicides (2,4-D-organophosphates, chlorophenols), solvents and organic chemicals (benzene, carbon tetrachloride), wood preservatives, dusts (wood, cotton), and some components in hair dye.
Chemotherapy and radiotherapy
Patients who receive cancer chemotherapy and/or radiation therapy are also at increased risk of developing NHL.
Several viruses have been implicated in the pathogenesis of NHL, including:
- EBV: EBV is a DNA virus that has been associated with Burkitt lymphoma, particularly in endemic areas of Africa; Hodgkin's disease; lymphomas in immunocompromised patients (i.e. organ transplantation and HIV infection); sinonasal lymphoma (Asia and South America); and sporadically in other B- and T-cell lymphomas. EBV can transform lymphocytes in culture. B lymphocytes from normal EBV-positive subjects grow as tumors in mice with severe combined immunodeficiency.
- HTLV-1: HTLV-1 is a human retrovirus that is endemic in certain areas of Japan and the Caribbean. HTLV-1 establishes a latent infection via reverse transcription in activated T-helper cells. A minority (5%) of carriers develop adult T-cell leukemia/ lymphoma. A HTLV-1 like provirus has been detected in some patients with mycosis fungoides, although conflicting findings have been reported.
HHV-8: Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8, or HHV- 8) KSHV-like DNA sequences are frequently detected in body cavity-based lymphomas in patients with HIV infection and in those with multicentric (plasma cell variant) Castleman's disease.
- HCV: Hepatitis C virus (HCV) infection is associated with the development of clonal B-cell expansions and certain subtypes of NHL, particularly in the setting of essential (type II) mixed cryoglobulinemia. HCV may predispose B cells to malignant transformation by enhancing signal transduction upon binding to the CD81 (TAPA-1) molecule.
HIV: NHL occurs in 2% to 3% of newly diagnosed AIDS cases. Pathologically, AIDS-related lymphomas are comprised of a narrow spectrum of histologic types consisting almost exclusively of B-cell tumors of aggressive type. These include: Diffuse large B-cell lymphoma, B-cell immunoblastic lymphoma, small noncleaved lymphoma, either Burkitt or Burkitt-like. The HIV-associated lymphomas can be categorized into: Aggressive B-cell lymphoma, primary central nervous system lymphoma (PCNSL), which represents 20% of all NHL cases in AIDS patients, primary effusion lymphoma, plasmablastic multicentric Castleman disease, Hodgkin's lymphoma.
- Borrelia burgdorferi: Infection with Borrelia burgdorferi, the etiologic agent in Lyme disease, has been detected in about 35% of patients with primary cutaneous B-cell lymphoma in Scotland. A near-complete clinical and histologic remission of a primary marginal zone B-cell lymphoma was observed after eradication of B burgdorferi with antibiotic treatment.
- H. pylori: The bacteria Helicobacter pylori has been shown to cause MALT in the digestive system in about 90% of cases.
Patients with congenital and acquired states of immunosuppression are at increased risk of NHL.
Congenital immunodeficiency states that are associated with an increased risk include ataxia- telangiectasia, Wiskott-Aldrich syndrome, common variable hypogammaglobulinemia, X-linked lymphoproliferative syndrome, and severe combined immunodeficiency.
- Acquired immunodeficiency states, such as HIV infection, iatrogenic immunosuppression (ie, organ or blood stem-cell transplantation recipients, long-term survivors of Hodgkin's disease), and a variety of collagen vascular and autoimmune diseases (eg, Sj