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SUMMARY
Lymphomas are a heterogeneous group of malignancies that originate from neoplastic transformation of lymphocytes that have undergone mutations that confer growth and survival advantages compared to their normal cellular counterparts.* These neoplasms usually originate in lymph nodes or lymphatic tissue in other sites (extranodal lymphoma), and can be localized or widespread at the time of diagnosis. Men are affected more frequently than women and the risk of acquisition of most lymphomas increases logarithmically with age. Classification systems have considered the likely lymphoid progenitor that corresponds to the phenotype (immunotype) and genotype of the malignant cells in the transformed clone. The specific pathologic diagnosis is usually established by the appearance of the histopathology in tissue sections, the immunophenotypic profile of CD antigens expressed on affected lymphocytes, specific cytogenetic findings, especially translocations (e.g., t[11;14]), immunocytochemical markers (e.g., cyclin D1), and the specific tissue location (e.g., mucosa-associated lymphatic tissue). Although most lymphomas arise without an evident cause, human T-cell leukemia/lymphoma virus I (HTLV-1), Epstein-Barr virus, hepatitis C virus, and human herpes virus-8 infections, as well as infections with the bacteria Helicobacter pylori and, perhaps, Chlamydophila psittaci, either are established as causal (e.g., HTLV-1) or have very strong associations with lymphoma incidence (hepatitis C virus), suggesting their role in causation. HIV is permissive by inducing severe immunodeficiency and setting the stage for an Epstein-Barr virus–induced or human herpes virus-8–induced lymphoma. These relationships may vary by geographic area. Several occupational and industrial exposures are suspected of being related to lymphoma incidence, for example, organochlorines, phenoxyacid herbicides, and others, but these associations have not been established with scientific certainty. At present, the estimated attributable risk of lymphoma from all suspected exogenous factors together is relatively small in proportion to the number of annual cases, leaving most cases without an apparent cause. There are wide discrepancies in the incidence of specific lymphoma subtypes in different geographic regions (e.g., follicular lymphoma is very common in the United States and very uncommon in East Asia). Primary extranodal lymphoma may involve virtually any tissue or organ. Depending on the site, important functional abnormalities may ensue (e.g., bilateral adrenal gland replacement and hypoadrenocorticism, hypothalamic–pituitary involvement and diabetes insipidus). Multidrug chemotherapy combinations in conjunction with lymphocyte-specific monoclonal antibody therapy form the foundation of current treatment paradigms for most lymphomas, though radiotherapy and surgical excision continue to play limited roles in selected circumstances, depending on the site and histopathology.
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Acronyms and Abbreviations
ALCL, anaplastic large cell lymphoma; ALK, ALCL tyrosine kinase gene; ATLL, adult T-cell leukemia/lymphoma; CBC, complete blood count; CRu, complete remission unconfirmed; CT, computed tomography; DLBCL, diffuse large B-cell lymphoma; EBV, Epstein-Barr virus; FDG,2-fluorodeoxyglucose; HHV-8, human herpesvirus-8; HL, Hodgkin lymphoma; HTLV-1, human T-cell leukemia/lymphoma virus-1; iFISH, interphase fluorescence in situ hybridization; Ig, immunoglobulin; IWG, International Working Group; MALT, mucosa-associated lymphatic tissue; NCCN, National Cancer Center Network; NHL, non-Hodgkin lymphoma; NK, natural killer; PET, positron emission tomography; R-CHOP, rituximab-cyclophosphamide, hydroxydoxorubicin, ...