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Non-Hodgkin's Lymphoma

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Cellular Classification of Adult NHL

    A pathologist should be consulted prior to a biopsy because some studies require special preparation of tissue (e.g., frozen tissue). Knowledge of cell surface markers and immunoglobulin and T-cell receptor gene rearrangements may help with diagnostic and therapeutic decisions. The clonal excess of light-chain immunoglobulin may differentiate malignant from reactive cells. Since the prognosis and the approach to treatment are influenced by histopathology, outside biopsy specimens should be carefully reviewed by a hematopathologist who is experienced in diagnosing lymphomas. Although lymph node biopsies are recommended whenever possible, sometimes immunophenotypic data are sufficient to allow diagnosis of lymphoma when fine-needle aspiration cytology is preferred.[1,2]

    Historical Classification Systems

    Historically, uniform treatment of patients with non-Hodgkin lymphoma (NHL) has been hampered by the lack of a uniform classification system. In 1982, results of a consensus study were published as the Working Formulation.[3] The Working Formulation combined results from six major classification systems into one classification. This allowed comparison of studies from different institutions and countries. The Rappaport classification, which also follows, is no longer in common use.

    Table 1. Historical Classification Systems for NHL

    Working Formulation[3]Rappaport Classification
    Low grade 
    A. Small lymphocytic, consistent with chronic lymphocytic leukemiaDiffuse lymphocytic, well-differentiated
    B. Follicular, predominantly small-cleaved cellNodular lymphocytic, poorly differentiated
    C. Follicular, mixed small-cleaved, and large cellNodular mixed, lymphocytic, and histiocytic
    Intermediate grade 
    D. Follicular, predominantly large cellNodular histiocytic
    E. Diffuse, small-cleaved cellDiffuse lymphocytic, poorly differentiated
    F. Diffuse mixed, small and large cellDiffuse mixed, lymphocytic, and histiocytic
    G. Diffuse, large cell, cleaved, or noncleaved cellDiffuse histiocytic
    High grade 
    H. Immunoblastic, large cellDiffuse histiocytic
    I. Lymphoblastic, convoluted, or nonconvoluted cellDiffuse lymphoblastic
    J. Small noncleaved-cell, Burkitt, or non-BurkittDiffuse undifferentiated Burkitt or non-Burkitt

    Current Classification Systems

    As the understanding of NHL has improved and as the histopathologic diagnosis of NHL has become more sophisticated with the use of immunologic and genetic techniques, a number of new pathologic entities have been described.[4] In addition, the understanding and treatment of many of the previously described pathologic subtypes have changed. As a result, the Working Formulation has become outdated and less useful to clinicians and pathologists. Thus, European and American pathologists have proposed a new classification, the Revised European American Lymphoma (REAL) classification.[5,6,7,8] Since 1995, members of the European and American Hematopathology societies have been collaborating on a new World Health Organization (WHO) classification, which represents an updated version of the REAL system.[9,10]

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