ALK and anaplastic large cell lymphoma: However, ALK+ cells are present in stem cell-enriched cord blood, and a study has identified a side population of cells in ALK+ ALCL cell lines and tumors with signatures similar to early thymic progenitors (ETPs), suggesting that transformation of T cells by NPM-ALK might occur early during thymic T cell development (Laurent et al., 2012; Moti et al., 2015).