Further analysis of the DN population based on CD25 and CD44 expression revealed that in tumor-free thymi, most ALK+ cells were DN3 (CD25+CD44−) and DN4 (CD25−CD44−) stage thymocytes, which correlates with the developmental stages at which Cd4 driven NPM-ALK expression was induced (Fig 2D). This evidence concerns the gene ALK and neoplasm.