Transcripts of the embryonic stem cell markers Oct4, Nanog, and - at low levels - Klf4 were detected in the four tumor cultures examined (one astrocytoma II, two astrocytoma III and one oligoastrocytoma III that yielded cell-forming spheres with extended self-renewal properties, Figure 4B). This evidence concerns the gene POU5F1 and astrocytoma (excluding glioblastoma).