الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The Hematological Malignancies are a group of neoplasms that arise through malignant transformation of bone marrow derived immune cells. The great diversity seen in this group of disorders is a reflection of the complexity of normal hematopoeisis and the immune system. Over the past 100 years a number of classifications have been devised in an attempt to subdivide hematological malignancies in a clinically and biologically relevant way. The primary basis of classification is the distinction between tumors of lymphocytes (the primary cell of the immune systems) and myeloid malignancies. Lymphoproliferative disorders are sub-classified used the World Health Organization (WHO) classification into 1) B-cell neoplasms, (2) T-cell and NK-cell neoplasms, and (3)Hodgkin lymphoma ; The classification of these disorders attempts to defines a number of clinico-pathological entities based on the stage of differentiation of the tumour cells as defined by their morphological appearances and expression of specific cell markers, the presence of genetic abnormalities in the cells and clinical features. The classification of these disorders attempts to identify the tumors’ putative cells of origin and their apparent maturity. Viruses, are among the few known causes of cancer and contribute to a variety of malignancies worldwide. The agents and hematological malignancies considered here are :Epstein-Barr virus (B-cell LPD; Burkitt lymphoma and many B-cell lymphomas arising in immunosuppressed or elderly patients ,It is also associated with extra nodal NK/T-cell lymphoma and found in many T-cell lymphoma); Kaposi’s Sarcoma Herpesvirus (multicentric castleman disease and primary effusion lymphomas); hepatitis C viruses (marginal zone lymphoma and Diffuse Large B-cell lymphoma);Human T-cell LeukemiaVirus1 (Adult T cell lymphoma/leukemia) and HIV(Non Hodgkin Lymphoma) according to the American Society of Clinical Oncology. In determining causality ,the criteria most often used are consistency of the association, either epidemiologic or on the molecular level, and oncogenicity of the agent in animal models or cell cultures. However use of these generally applied criteria in deciding on causality is selective, and the criteria may be weighted differently. whereas for most of the tumor viruses the viral genome persists in an integrated or episomal form with a subset of viral genes expressed in the tumor cells,some agents are not inherently oncogenic ,but infection leads to transformation of cells by indirect means. For some malignancies the viral agent appears to serve as a cofactor. The suspicion of an infectious etiology to HL is almost as old as the recognition of the disease as such. Accordingly, both the disease’s typical histological presentation dominated by inflammatory cells and its typical clinical presentation with sudden onset of fever, night sweats and lymphadenopathy would be compatible with an infectious process. Non Hodgkin’s lymphoma (NHL) comprises numerous distinct entities, whose epidemiology may differ considerably. Importantly, these epidemiological differences often reflect different etiologies and different natural histories. EBV is an example of a transforming virus and in addition to HL it has been implicated in several forms of NHL .Also noteworthy are two other transforming viruses, human T lymphotropic virus type I (HTLV-I) and human herpesvirus 8 (HHV8) which is evolutionarily related to EBV. HCV is usually acquired through blood-borne exposures, It produces chronic hepatitis and viraemia following primary infection. Ongoing HCV infection is associated with the development of essential mixed cryogrobulinaemia, a low-grade lymphoproliferative disorder that can progress to NHL. A mechanism, unique to HIV-1 infection, is induction of immune suppression through profound depletion of CD4+ T lymphocytes, leading to the condition known as AIDS. AIDS is associated with a markedly elevated risk for several types of lymphoma, including in particular high-grade B cell NHLs. There is no doubt about the value and potential of using molecular techniques in diagnostic virology. This does not apply solely to the detection and analysis of those viruses that cannot be isolated in cell cultures, such as hepatitis C. Molecular amplification methods, as PCR or RT-PCR, offer such greatly increased sensitivity and specificity.