t(1;2)(q21;p23) and t(2;3)(p23;q21): Two novel variant translocations of the t(2;5)(p23;q35) in anaplastic large cell lymphoma

Cytogenetic investigations in two cases of anaplastic large cell lymphoma ( ALCL) showed novel variants of the classical (2;5)(p23;q35) translocation, namely a t(1;2)(q21;p23) and a t(2;3)(p23;q21). The tumor cells in both cas es gave positive immunohistochemical labeling for ALK protein (with both mo noclonal and polyclonal antibodies), demonstrating that these translocation s induce aberrant expression of this kinase and suggesting that genes other than NPM can activate the ALK gene in ALCL. These two cases were shown by an in vitro kinase assay to express ALK kinases (104 kD and 97 kD, respecti vely), which differed in size from the classical NPM-ALK fusion product (80 kD). Moreover, ALK expression was confined to the cytoplasm of the tumor c ells in each case, supporting the hypothesis that the observed nuclear loca lization of NPM-ALK in classical ALCL is not the site of oncogenic activity of the ALK kinase. (C) 1999 by The American Society of Hematology.