Aleukemic granulocytic sarcoma with AML1/ETO fusion gene expression and clonal T cell populations.

We report a unique case of aleukemic granulocytic sarcoma of the neck, originally misdiagnosed as non-Hodgkin's lymphoma (NHL), though chloroma was also suspected due to a greenish macroscopic appearance and the presence of myeloid chloroacetate esterase (CAE)+ cells. The proof of clonal T cell receptor gamma chain (TcRgamma) gene rearrangements in the recurring tumor was deemed to confirm the initial diagnosis of T cell NHL. Altogether five distinct types of clonal TcRgamma gene rearrangements were found in the tumor, bone marrow and peripheral blood. Only retrospectively, using RT-PCR, did we detect the acute myeloid leukemia subset-specific fusion gene AML1/ETO in the frozen samples of the relapsed tumor, as well as in the otherwise unaffected bone marrow and peripheral blood (representing 'minimal initial disease' in the latter two samples). Simultaneous staining verified that the neoplastic CAE+ cells and CD45RO+ T cells were different populations.