LEF1 and TCF7 promoters were significantly hypermethylated in ALCL tumors compared to AITLs and to normal T cells, but no significant differences in DNA methylation levels were observed between ALCL and PTCL-NOS samples, most likely due to heterogeneity in the PTCL-NOS DNA methylation levels that is reflective of the diversity of this “wastebasket” disease category. This evidence concerns the gene TCF7 and mature T-cell and NK-cell non-Hodgkin lymphoma.