To validate our findings from cell lines engineered to overexpress STAT3, we tested 7 different NK cell leukemia/lymphoma cell lines with either WT STAT3 (KAI3, NK-92, KHYG-1 and NKL), or naturally occurring STAT3 mutations (YT and NK-YS, Y640F mutation; SNK6, D661V mutation) [29-31]. This evidence concerns the gene STAT3 and aggressive NK-cell leukemia.