Lineage alteration in precursor B cell acute lymphoblastic leukemia following T cell lymphoblastic lymphoma

A 10-year-old girl was diagnosed with lymphoblastic lymphoma; staging evaluation revealed a large mediastinal mass and normal peripheral blood and bone marrow morphology. Tumor cell immunologic marker analysis and Southern blot gene rearrangement studies demonstrated a T-cell lineage. She achieved a complete remission following multi-agent chemotherapy; however, 19 months following initial diagnosis while on maintenance therapy, she presented with typical acute lymphoblastic leukemia (ALL). The bone marrow was replaced by lymphoblasts, though the mediastinum was normal and there was no peripheral lymphadenopathy. Repeat immunophenotypic and genotypic studies demonstrated a precursor B-cell ALL lineage without expression of the T-cell surface antigens present on the original neoplasm. Repeat genotypic analysis showed immunoglobulin heavy and light chain gene rearrangements without the T-cell receptor gamma and beta gene rearrangements noted in the original lymphoblastic lymphoma. The complete alteration of lineage in these lymphoblastic processes suggests the de novo occurrence of a second neoplasm or, alternatively, an ALL relapse from a lineage-uncommitted neoplastic lymphoid progenitor cell.