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

A variable fraction of anaplastic large-cell lymphomas (AL-CLs) exhibits a t(2;5)(p23;q35) translocation that results in expression of the chimeric hy perphosphorylated protein NPM-ALK (p80). Tumor cells expressing NPM-ALK exh ibit markedly enhanced proliferative activity, but comparative cellular kin etic studies on ALK(+) (ALK lymphomas) and ALK-lymphomas are lacking. The p resent study showed that ALK(+) lymphomas, detected with the monoclonal ant ibody ALKc (n = 17), had significantly higher average values for the prolif eration-associated parameters mitotic index, ana/telophase index, growth in dex (x 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 cycl e-regulatory protein p34(cdc2) than did ALK(-) ALCLs (n = 15). Whether this intense proliferative activity contributes to the good response to chemoth erapy and favorable outcome of ALK+ ALCLs remains to be assessed in a large r series of patients. Our findings support the notion that ALK(+) and ALK(- ) ALCLs are 2 distinct disease entities. (C) 2000 Wiley-Liss, Inc.