Expression of the ALK protein by anaplastic large‐cell lymphomas correlates with high proliferative activity

A variable fraction of anaplastic large‐cell lymphomas (ALCLs) exhibits a t(2;5)(p23;q35) translocation that results in expression of the chimeric hyperphosphorylated protein NPM‐ALK (p80). Tumor cells expressing NPM‐ALK exhibit markedly enhanced proliferative activity, but comparative cellular kinetic studies on ALK+ (ALK lymphomas) and ALK– lymphomas are lacking. The present study showed that ALK+ lymphomas, detected with the monoclonal antibody ALKc (n = 17), had significantly higher average values for the proliferation‐associated parameters mitotic index, ana/telophase index, growth index (x × mitotic index – apoptotic index, assuming x = 3), percentages of Ki‐67+ cells and fraction of cells expressing cyclin A or B or the cell cycle–regulatory protein p34cdc2 than did ALK– ALCLs (n = 15). Whether this intense proliferative activity contributes to the good response to chemotherapy and favorable outcome of ALK+ ALCLs remains to be assessed in a larger series of patients. Our findings support the notion that ALK+ and ALK– ALCLs are 2 distinct disease entities. Int. J. Cancer 86:777–781, 2000. © 2000 Wiley‐Liss, Inc.