Cytomorphology and molecular characterization of CLTC-ALK rearrangement in 2 cases of ALK-positive diffuse large B-cell lymphoma with extensive bone marrow involvement

Aanaplastic lymphoma kinase (ALK)-positive diffuse large B-cell lymphoma (DLBCL) is an unusual disease entity first reported in 1997 as DLBCL with expression of full-length ALK protein. The World Health Organization classification enlists the disease as a rare variant of DLBCL. Herein we describe two cases of ALK-positive DLBCL with cytomorphologic and molecular characteristics for the first time in Korea. The patients were 35-yr-old and 24-yr-old male patients. Immunohistochemical studies on the lymph nodes revealed large sized neoplastic cells with plasmablastic differentiation, which were negative for CD30 and positive for ALK with the characteristic granular staining in the cytoplasmic region. Extensive involvement of bone marrow was observed in both cases showing large, extremely atypical cells. Fluorescence in situ hybridization and molecular studies on the bone marrow aspirate specimens led to the detection of a clathrin (CLTC)/ALK rearrangement, Despite aggressive chemotherapy, the patients died 15 and 17 months after the diagnosis, indicating poor prognosis of the disease entity. This is the first report demonstrating the cytomorphologic findings of ALK-positive DLBCL cells on bone marrow aspirates.