Thymic lymphoblastic lymphoma of committed natural killer cell precursor origin: a case report.

BACKGROUND

Recently, it was demonstrated that the human fetal thymocyte contains a bipotential progenitor capable of both T lymphocyte and natural killer (NK) cell differentiation. However, prior to this report a malignant neoplasm arising from these cells had not been documented.

METHODS

A Japanese female age 38 years was examined by morphology of light and electron microscopy, immunohistochemistry, 3-color flow cytometry, cytotoxic assay, and Southern blotting.

RESULTS

The patient presented with a mediastinal mass and pleural effusion. Leukemic progression was identified following chemotherapy and complete clinical remission. Immunophenotyping of lymphoma revealed CD45++, c-kit dim+, terminal deoxynucleotidyl transferase (TdT)-<+, CD38++, CD34+<++, CD33+<-, CD13dim+approximately+, HLA-DR+, CD7+, cytoplasmic CD3 (cCD3)+, surface CD3 (sCD3)-, CD2dim+, CD56+, CD16-, CD11b+, CD57-, CD1a-, CD5-, TCR alpha beta-, TCR gamma delta-, CD4-, CD8-, CD28-, CD10-, CD19-, CD20-, CD22-, surface immunoglobulins-, and CD14-. Functional NK activity of the lymphoma cells was extremely low. DNA analysis revealed no gene rearrangement in TCR beta, gamma, and delta or immunoglobulin heavy and light chain genes.

CONCLUSIONS

Lymphoma cells of this case were derived from a distinct subtype of lymphocyte that originate from a thymic precursor committed to NK cell differentiation. This category is different from those of thymic T or precursor B cell pheno-/genotype.