Cellular Classification and Biologic Correlates
Hodgkin lymphoma can be divided into two broad pathologic classes:[1,2]
- Classical Hodgkin lymphoma.
- Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL).
Classical Hodgkin Lymphoma
Classical Hodgkin lymphoma is divided into four subtypes:
- Lymphocyte-rich classical Hodgkin lymphoma (LRCHL).
- Nodular sclerosis Hodgkin lymphoma (NSHL).
- Mixed-cellularity Hodgkin lymphoma (MCHL).
- Lymphocyte-depleted Hodgkin lymphoma (LDHL).
These subtypes are defined according to the number of Reed-Sternberg (R-S) cells, characteristics of the inflammatory milieu, and the presence or absence of fibrosis.
The hallmark of classic Hodgkin lymphoma is the R-S cell.[3] This is a binucleated or multinucleated giant cell that is often characterized by a bilobed nucleus, with two large nucleoli, giving an owl's eye appearance to the cells. A striking characteristic is the rarity (about 1%) of the malignant R-S cell in specimens and the abundant reactive cellular infiltrate of lymphocytes, macrophages, granulocytes, and eosinophils. R-S cells generally do not express B-cell antigens such as CD45, CD19, and CD79A. Almost all patients express CD30, and approximately 70% of patients express CD15. CD20 is expressed in approximately 5% to 10% of cases.[4,5,6] R-S cells show constitutive activation of the nuclear factor kappa B pathway, which may prevent apoptosis and provide a survival advantage. Most cases of classic Hodgkin lymphoma are characterized by expression of tumor necrosis factor receptors (TNF-Rs) and their ligands, as well as an unbalanced production of Th2 cytokines and chemokines. Activation of TNF-R results in constitutive activation of nuclear factor kappa B.[7]
The histologic features and clinical symptoms of Hodgkin lymphoma have been attributed to the numerous cytokines, chemokines, and products of the TNF-R family [8] secreted by the R-S cells. Interleukin-5 could be responsible for the eosinophilia in MCHL, and transforming growth factor-beta for the fibrosis in the NSHL subtype.
- In the United States, NSHL histology accounts for approximately 85% of Hodgkin lymphoma cases in older children and adolescents but only 50% of cases in younger children. This subtype is distinguished by the presence of collagenous bands that divide the lymph node into nodules, which often contain an R-S cell variant called the lacunar cell. Some pathologists subdivide nodular sclerosis into two subgroups (NS-1 and NS-2) on the basis of the number of R-S cells present.
- In the United States, MCHL histology is more common in younger children than in adolescents or adults. In a Children's Cancer Group (CCG) study, MCHL accounted for 30% of cases in children younger than 10 years. R-S cells are frequent in a background of abundant normal reactive cells (lymphocytes, plasma cells, eosinophils, and histiocytes). This subtype can be confused with non-Hodgkin lymphoma.
- LRCHL may have a nodular appearance, but immunophenotypic analysis allows distinction between this form of Hodgkin lymphoma and nodular lymphocyte-predominant disease.[9] LRCHL cells express CD15 and CD30 while NLPHL almost never expresses CD15.
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