Using DNA methylation profiling it has been discovered that ALK- and ALK+ ALCL have highly similar genome-wide DNA methylation in the genes involved in T-cell differentiation and immune responses (TCR, CTLA-4) and these methylation patterns resemble those of thymic progenitor cells, suggesting a possible thymic origin of ALCL: a double-positive CD4/CD8 precursor T-cell for ALK- ALCL and a CD34+/CD1a− precursor T-cell for ALK+ ALCL [65] (Figure 8). Here, CD4 is linked to anaplastic large cell lymphoma.