What is the role of genetics in the etiology of pediatric non-Hodgkin lymphoma (NHL)?

Updated: Jun 14, 2018
  • Author: J Martin Johnston, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Answer

The genetic basis of pediatric non-Hodgkin lymphoma has been studied extensively. [16] Each subtype of non-Hodgkin lymphoma is characterized by 1 or more molecular alterations that contribute to the malignant phenotype. Many of these alterations are chromosomal translocations involving genes for immunoglobulin or T-cell receptor (TCR) molecules.

During normal lymphocyte development, these loci undergo recombination that enhances immunologic diversification. However, mistargeted recombination leads to translocations with other genes, typically those that regulate cell growth. The resulting dysregulation of these other genes contributes to the transformed phenotype.

For example, the hallmark of Burkitt lymphoma is a t(8;14)(q24;q32) translocation, which is observed in approximately 80% of patients. This translocation juxtaposes c-myc, which encodes a transcription factor important in initiation of the cell cycle, with the locus for the immunoglobulin heavy chain. Less commonly, c-myc is adjoined to the gene encoding the immunoglobulin kappa light chain [t(2;8)(p11;q24)] or the lambda light chain [t(8;22)(q24;q11)].

In all 3 instances, the result is aberrant expression of the c-MYC protein under the influence of regulatory sequences of immunoglobulin genes. This aberration contributes to the pathogenesis of Burkitt lymphoma. [17]

Aside from the t(8;14) translocation, Burkitt lymphoma frequently involves a gain of chromosomal material that can affect any of a number of chromosomes. Abnormalities of chromosomal arms 1q, 7q, or 13q may portend a poor prognosis. [17, 18]

A small portion of T-lymphoblastic lymphomas are also associated with translocations involving one of the TCR loci; either TCR alpha delta (14q11) or TCR beta (7q34). The most common example (observed in 7% of children with T-lymphoblastic lymphomas) is the t(11;14)(p13;q11) translocation, which enhances expression of the LMO2 gene on chromosome 11. This gene encodes LIM protein, an apparent modulator of gene transcription.

A more common abnormality observed in T-lymphoblastic lymphoma is a deletion in a regulatory region of the gene TAL1. This deletion, which is too small to be detected with conventional cytogenetic techniques, leads to aberrant expression of Tal-1, another transcriptional regulator.

Inactivation of the multiple tumor-suppressor gene 1 (MTS-1/p16INK4 alpha/CDKN2) on chromosome 16 has been identified as a common genetic event in T-cell ALL; its frequency in T-lymphoblastic lymphoma is likely to be a significant factor. Of interest, the deletions or disruptions responsible for this inactivation are apparently related to illegitimate activity of the same V(D)J recombinase that mediates recombination of the TCR gene. [19] Thus, even in the absence of a TCR translocation, similar molecular mechanisms may be responsible for disrupting other genes involved in normal control of the cell cycle.

Some B-lineage LCLs have the same t(8;14)(q24;q32) translocation observed in Burkitt lymphoma. Compared with adults with B-LCL, this appears to be more common in children and may portend a worse prognosis. [20] Alternatively, most anaplastic (T-lineage) LCLs in children involve a t(2;5)(p23;q35) translocation. This change joins the nucleophosmin gene (NPM) on chromosome 5 to a gene called anaplastic lymphoma kinase (ALK) on chromosome 2 and allows for the expression of p80, an NPM/ALK fusion protein.

Rarely, anaplastic LCLs exhibit rearrangements of c-myc; based on small numbers of patients, this appears to confer a poor prognosis. [21, 22]

Transcripts of NPM/ALK are also observed in about 20% of individuals with non-Hodgkin lymphoma lacking cytogenetic evidence of t(2;5); this finding reflects an occult or variant translocation. [23] Patients with non-Hodgkin lymphomas expressing p80 may have a survival advantage over patients whose lymphomas lack p80. [24]


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