Malignant non-Hodgkin's lymphomas in children.

The spectrum of non-Hodgkin's lymphomas (NHL) that occurs in children differs markedly from that in adults. This is probably a consequence of differences in the proportions of precursor and mature lymphoid cells in the immune systems of children and adults, and the greater emphasis on the development of an immunologic repertoire in the child. Childhood NHL can be classified into three main types based on histology, all of them diffuse: lymphoblastic, small noncleaved cell, and large cell. The majority of lymphoblastic lymphomas are of immature T cell (thymocyte) origin, although a few have a B cell precursor phenotype. All express the enzyme terminal transferase. Small noncleaved lymphomas express B cell characteristics, as do the majority do the majority of large cell lymphomas, although a small proportion of the latter express T cell characteristics. Very few are of true histiocytic origin. Little is known of the epidemiology of lymphoblastic and large cell lymphomas. However, using histology as a diagnostic criterion, both occur throughout the world and occur primarily, as do all childhood NHL, in the first two decades of life. There appear to be at least two types of small noncleaved cell lymphomas, both of which are associated with specific chromosomal translocations. An endemic form occurs at high frequency in equatorial Africa, and a sporadic form occurs at low frequency throughout the world. The endemic tumor is associated with the Epstein-Barr virus, it has a high incidence of jaw tumors, and has a breakpoint on chromosome 8 that is usually some distance upstream of the c-myc oncogene. The sporadic tumor is only occasionally associated with EBV, it often involves the bone marrow, particularly at relapse, and has a breakpoint on chromosome 8 that is usually very close to or within the c-myc oncogene. Childhood NHL is rarely truly localized, and treatment regimens are always based on chemotherapy. There is no evidence that radiation is beneficial when modern combination drug regimens are employed as the primary therapeutic modality. Prophylactic treatment to the central nervous system is recommended in nearly all patients, and intrathecal drugs, usually supplemented by some form of high-dose or intermediate-dose methotrexate, appear to represent adequate prophylaxis to the CNS. The most effective regimens result in cure in almost all patients who have limited overt disease, and in a high proportion (50 to 75 per cent) of patients with extensive disease, although patients with bone marrow involvement do poorly with most regimens.(ABSTRACT TRUNCATED AT 400 WORDS)