Is B-Lineage Acute Lymphoblastic Leukemia With a Mature Phenotype and L1 Morphology a Precursor B-Lymphoblastic Leukemia/Lymphoma or Burkitt Leukemia/Lymphoma?

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Abstract
Context.—B-lineage acute lymphoblastic leukemia (ALL) with a mature phenotype and L1 morphology is a rare condition that may pose a diagnostic and management challenge. Objective.—To report our experience with 2 such unusual cases of pediatric B-lineage ALL. Design.—Morphologic, immunophenotypic, and cytogenetic features of the leukemic blast cells were reviewed in conjunction with clinical and other laboratory findings. Results.—The leukemic blast cells in both cases were small to medium with scant basophilic cytoplasm and several small inconspicuous nucleoli, characteristic of L1 lymphoblasts. Immunophenotypically, they were positive for CD19, CD22, and low-density CD20, with expression of surface immunoglobulin λ light chain. They were negative for immature (CD34 and terminal deoxynucleotidyl transferase), myeloid, and T-cell–associated markers. Conventional cytogenetic and fluorescent in situ hybridization studies failed to demonstrate chromosomal translocations involving the c-myc gene. Both patients were treated with Children's Cancer Group ALL protocols and had good responses. Conclusions.—B-lineage ALL with a mature phenotype, L1 morphology, and absent chromosomal translocations involving the c-myc gene is best classified and managed as precursor B-lymphoblastic leukemia/lymphoma instead of Burkitt leukemia/lymphoma.