Non-Hodgkin lymphoma

Since the late 1960s, treatment outcomes for pediatric patients with non-Hodgkin lymphoma have steadily improved. Even for patients with advanced disease, event-free survival rates are now 65-90%. (See Prognosis, Treatment, and Medication.) The mainstay of conventional therapy is multiagent chemotherapy tailored to the histologic subtype and the clinical stage of disease. In certain individuals with non-Hodgkin lymphoma, surgical resection and radiation therapy are also key components of definitive treatment. Newer therapies that target immunologic and biologic aspects of the lymphoma are still under development but beginning to appear in the clinical arena. (See Treatment and Medication.) Lymphomas are malignant neoplasms of lymphoid lineage. Broadly classified as either Hodgkin disease (Hodgkin's disease) or as non-Hodgkin lymphoma, lymphomas are clinically, pathologically, and biologically distinct (see the image below). (See Prognosis and Workup.)[1, 2] Massive mediastinal T-lymphoblastic lymphoma. NoteMassive mediastinal T-lymphoblastic lymphoma. Note compression of the left mainstem bronchus and the pulmonary atelectasis. According to the National Cancer Institute (NCI) formulation, most childhood non-Hodgkin lymphomas can be classified as one of the following types: Lymphoblastic lymphomas Small noncleaved cell lymphomas (SNCCLs) - Burkitt lymphomas and non-Burkitt lymphomas (Burkittlike lymphomas) Large cell lymphomas (LCLs) B-cell LCLs and anaplastic (usually T-cell) LCLs (ie, Ki-1+ lymphomas) have come to be viewed as distinct entities. In this article, these categories are considered separately. Other, less common forms of childhood lymphoma (some of which are much more common in adults) are not discussed. Disease progression Most malignancies arise as disease localized in the organ or tissue of origin. They may then secondarily spread by means of local extension or distant metastases. In contrast, non-Hodgkin lymphoma is best regarded as a systemic disease, because of the unique anatomy of the lymphoid system and because of the physiology of lymphoid cells, which tend to migrate whether they are normal or malignant. The role of lymphoma stem cells in the genesis and maintenance of B-cell lymphomas remains speculative.(See Etiology.)[3] Non-Hodgkin lymphoma versus acute leukemia Childhood non-Hodgkin lymphoma generally manifests as bulky extramedullary (usually extranodal) disease with or without demonstrable dissemination. The distinction between non-Hodgkin lymphoma and acute leukemia is arbitrary. Therefore, these entities are best considered in terms of a spectrum ranging from clinically localized disease to overt leukemia. In most treatment protocols, acute leukemia is now defined on the basis of marrow involvement above some threshold (typically, a blast count of >25%) irrespective of the presence of bulky extramedullary disease. In contrast, an extramedullary tumor accompanied by marrow involvement below this threshold constitutes stage 4 lymphoma.