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
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
- 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),
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)
Small lymphocytic type
- The main gene involved is bcl-3 located on chromosome 19.
- The translocation found in small lymphocytic lymphoma is
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).
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).
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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,
- 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
- 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,
- 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, Sjögren?s syndrome, rheumatoid vasculitis and Felty?s syndrome,
systemic lupus erythematosus, chronic lymphocytic thyroiditis, and
angioimmunoblastic lymphadenopathy) also pose an increased risk of
An increased incidence of GI lymphomas is seen in patients with
celiac (nontropical) sprue and inflammatory bowel disease,
particularly Crohn?s disease. An aberrant clonal intraepithelial
T-cell population can be found in up to 75% of patients with
refractory celiac sprue prior to the development of overt T-cell
lymphoma using immunophenotyping and T-cell receptor gamma gene
rearrangement PCR techniques.
Gastric mucosa-associated lymphoid
tissue (MALT) lymphoma is seen most frequently, but not exclusively,
in association with Helicobacter pylori infection.
In contrast to
studies performed in European patients, Mexican patients with
intestinal lymphomas show a high frequency of EBV positivity; this
finding is not limited to T-cell NHLs but rather includes a
significant portion of B-cell NHLs.
Recent studies indicate that
Campylobacter jejuni and immunoproliferative small intestinal
disease (α-chain disease) are related.
Ocular adnexal lymphoma
A report from the National Cancer
Institute, Aviano, Italy, notes an association between infection
with Chlamydia psittaci and ocular adnexal lymphoma.
The infection was found to be highly specific and does not reflect a subclinical infection widespread among the general population.