Although KIT mutations are present in 20–25% of cases of t(8;21)(q22;q22) acute myeloid leukemia (AML), concurrent development of systemic mastocytosis (SM) is exceedingly rare. We examined the clinicopathologic features of SM associated with t(8;21)(q22;q22) AML in ten patients (six from our institutions and four from published literature) with t(8;21) AML and SM. In the majority of these cases, a definitive diagnosis of SM was made after chemotherapy, when the mast cell infiltrates were prominent. Deletion 9q was an additional cytogenetic abnormality in four cases. Four of the ten patients failed to achieve remission after standard chemotherapy and seven of the ten patients have died of AML. In the two patients who achieved durable remission after allogeneic hematopoietic stem cell transplant, recipient-derived neoplastic bone marrow mast cells persisted despite leukemic remission. SM associated with t(8;21) AML carries a dismal prognosis; therefore, detection of concurrent SM at diagnosis of t(8;21) AML has important prognostic implications.

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.