ALK and anaplastic large cell lymphoma: However, our findings, which are based on comparison of DNA methylation patterns among different T cell differentiation stages, indicate that T cell transformation in ALK+ ALCL may occur in progenitor cells rather than in mature T cells and are in line with two papers reporting that ALCLs have a primitive origin and arise in thymocytes before TCR β-rearrangement (Malcolm et al., 2016; Moti et al., 2015).