PROM1 and neoplasm: In malignant rhabdoid tumor of the kidney (MRTK), a very aggressive malignancy in infants, Yanagisawa et al. found that as few as 1,000 CD133+ MRTK cells were able to initiate tumors in NOD/scid mice, yet the metastatic potential of these cells was unaffected compared to CD133- cells, leading the authors to conclude that CD133+ cells may determine metastatic fate of MRTK cells and CD133- may support tumor progression and metastasis [45].