Composite small lymphocytic lymphoma and extra-medullary myeloid tumor: a potential diagnostic pitfall

Reported herein is a case of composite small lymphocytic lymphoma (SLL) and extramedullary myeloid tumor (EMT) occurring in the same lymph node. Routine morphologic examination revealed a diffuse proliferation of small mature lymphocytes with numerous irregularly dispersed nodules, closely resembling SLL with prominent proliferation centers or Richter's transformation. Flow cytometric immunophenotyping and immunohistochemical stains demonstrated the presence of SLL cells as well as myeloblasts, confirming the diagnosis of a composite SLL and EMT. Conventional cytogenetics and fluorescence in situ hybridization studies revealed inversion 16 chromosome involving the core binding factor beta and myosin heavy chain 11 genes, characteristic of acute myeloid leukemia with abnormal bone marrow eosinophils and inv(16) or t(16;16) [CBFbeta/MYH11]. In conclusion, the occurrence of SLL and EMT in the same lymph node is rare and multiparameter approach is essential for a definitive diagnosis.