We investigated whether phosphorylated STAT3 could help with the differential diagnosis and serve as a predictive biomarker by studying the expression of pSTAT3-Y705 and -S727 in 89 cases of ALK+/- ALCL and PTCL, NOS, including 10 cases of CD30high PTCL, NOS. This evidence concerns the gene ALK and mature T-cell and NK-cell non-Hodgkin lymphoma.