The distinction between Burkitt and Burkitt-like lymphoma/leukemia is controversial. Burkitt lymphoma consists of uniform, small, noncleaved cells, whereas Burkitt-like lymphoma is a highly disputed diagnosis among pathologists because of features that are consistent with DLBCL. Cytogenetic evidence of c-myc rearrangement is the gold standard for diagnosis of Burkitt lymphoma. For cases in which cytogenetic analysis is not available, the WHO has recommended that the Burkitt-like diagnosis be reserved for lymphoma resembling Burkitt lymphoma or with more pleomorphism, large cells, and a proliferation fraction (i.e., Ki-67[+] of ?99%). Studies have demonstrated that the vast majority of Burkitt-like or "atypical Burkitt" lymphomas have a gene expression signature similar to Burkitt lymphoma. Additionally, as many as 30% of pediatric DLBCL cases will have a gene signature similar to Burkitt lymphoma.[13,14] Despite the histologic differences, Burkitt and Burkitt-like lymphoma/leukemia are clinically very aggressive and are treated with very aggressive regimens.[15,16,17,18]
Diffuse large B-cell lymphoma
DLBCL is a mature B-cell neoplasm that represents 10% to 20% of pediatric NHL.[2,3,19] DLBCL occurs more frequently during the second decade of life than during the first decade.[2,20,21] The WHO classification system does not recommend morphologic subclassification based on morphologic variants (e.g., immunoblastic, centroblastic) of DLBCL. Pediatric DLBCL may present clinically similar to Burkitt or Burkitt-like lymphoma, though it is more often localized and less often involves the bone marrow or CNS.[19,20,23]
With the exception of primary mediastinal B-cell lymphoma, DLBCL in children and adolescents differs biologically from DLBCL in adults. The vast majority of pediatric DLBCL cases have a germinal center B-cell phenotype, as assessed by immunohistochemical analysis of selected proteins found in normal germinal center B cells.[21,24,25] Unlike adult DLBCL of the germinal center B-cell type, in which the t(14;18) translocation involving the immunoglobulin heavy-chain gene and the BCL2 gene is commonly observed, pediatric DLBCL rarely demonstrates the t(14;18) translocation. As many as 30% of patients younger than 14 years with DLBCL will have a gene signature similar to Burkitt lymphoma. Outcomes for children with DLBCL are more favorable than those observed in adults, with overall 5-year event-free survival rates of approximately 90% in children.[16,17,18] Outcome appears to be lower for pediatric patients with DLBCL who have chromosomal rearrangement at MYC (8q24).
About 20% of pediatric DLBCL presents as primary mediastinal disease (primary mediastinal B-cell lymphoma [PMBCL]). This presentation is more common in older children and adolescents and is associated with an inferior outcome compared with other pediatric DLBCL.[16,17,20,26,27] PMBCL is associated with distinctive chromosomal aberrations (gains in chromosome 9p and 2p in regions that involve JAK2 and c-rel, respectively)  and commonly shows inactivation of SOCS1 by either mutation or gene deletion.[28,29] PMBCL also has a distinctive gene expression profile in comparison with other DLBCL, suggesting a close relationship of PMBCL with Hodgkin lymphoma.[30,31]