Sea-Blue Histiocytosis of Bone Marrow in a Patient with t(8;22) Acute Myeloid Leukemia

An 80-year-old Japanese male was treated with chemotherapy consisting of cyclophosphamide, doxorubicin, vincristine, and prednisolone, for non-Hodgkin lymphoma. Nine months after the chemotherapy, he was diagnosed with acute myeloid leukemia (AML) (M4) with translocation 8p11 and 22q13. The patient bone marrow indicated a remarkable degree of sea-blue histiocytosis. His disease was aggressive, and he died of the disease. Sea-blue histiocytes are macrophages harboring blue vacuoles and granular deposition, which results from the phagocytosis of dead cells and the subsequent deposition of phospholipids. AML with the t(8; 22) (p11; q13) translocation is a rare subtype of AML, which is a rare translocation with a prevalence of less than 1.0% among all AML cases. The oncogenesis of t(8; 22) (p11; q13) is caused by the fusion protein monocytic leukemia zinc finger protein (MOZ) and transcription factor p300. MOZ can be fused to various translocation targets including CBT, TIF2, and p300, corresponding to t(8; 16), inv(8), and t(8; 22), respectively. This subgroup of AML reveals the hallmarks of the disease, including monocytic arrest and erythro/hemophagocytosis by blasts. A substantial proportion of the AML M4/M5 subtype harboring MOZ as an aberrant fusion gene represents erythrophagocytosis. Although rare, t(8; 22) is very specific to the AML M4/M5 subtype and seems to represent sea-blue histiocytosis as one of the characteristic features of monocytic AML with macrophage activation. Thus, sea-blue histiocytes are considered to be one of hallmarks in monocytic AML with MOZ translocation.