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Non-Hodgkin lymphoma rarely presents as an extranodal lymphoma that is restricted to the CNS known as primary CNS lymphoma (PCNSL). PCNSL can affect multiple parts of the neuraxis including the eyes, brain, leptomeninges, or spinal cord and accounts for approximately 3% of all the primary CNS tumors diagnosed each year in the United States. Between 1970 and 2000, the incidence of PCNSL increased largely due to the HIV pandemic. However, the incidence has stabilized or decreased over the last decade to about 0.47 cases per 100,000 persons [1,2]. Congenital or acquired immunodeficiency is the only established risk factor for PCNSL and HIV-infected individuals are at greater risk of developing this tumor. Approximately 2–13% of patients with a previous diagnosis of AIDS develop PCNSL. [ABSTRACT FROM AUTHOR]

Non-random chromosomal abnormalities are a common feature of many hematolymphoid disorders and are a key component of their pathogenesis. As such, routine chromosome analysis is critical in the laboratory workup of most known or suspected myelodysplastic/myeloproliferative disorders, leukemias, and lymphomas. Such studies can provide (1) diagnostic confirmation; (2) information useful for classification, staging, and prognostication; (3) information to guide appropriate choice of therapy; and (4) evidence of remission or relapse. In lymph node evaluation, cytogenetics can differentiate a reactive process from a malignant condition. [ABSTRACT FROM AUTHOR]

A critical review of the neoplastic disorders of hematopoietic cells has been conducted by panels of expert clinicians and pathologists under the sponsorship of the World Health Organization (WHO), and from this effort a comprehensive classification for these disorders has been developed. Clinical features, phenotypic characteristics of the cellular proliferations, and, in many instances, genotypic features of the abnormal cells are all used in characterizing these disorders. Detailed descriptions and discussions of diagnostically important features for the entities defined within this classification have been summarized and published in a monograph – WHO Classification of Tumors of Haematopoietic and Lymphoid Tissues [1] – which represents the consensus of the many experts who have contributed to the WHO project. [ABSTRACT FROM AUTHOR]