KRT6B and neoplasm: Although Ddx4 was not investigated in these studies, the niche-forming cells expressed stem or progenitor cell markers such as ALDH1, leucine-rich repeat-containing G-protein coupled receptor-5 (LGR-5), lymphoid enhancer binding factor-1 (LEF-1), CD133, and cytokeratin-6B (CK-6B), and were able to generate tumor spheres in vitro.