Both papers indicate that a single mutation in normal intestinal stem cells can give rise to tumours, as has been suggested. It is interesting that, although LGR5 and PROM1 seem to mark similar stem cells in the small intestine, PROM1 does not mark colonic stem cells, whereas LGR5 does. This illustrates the need to clearly define markers and their limitations if we are to begin to understand the contribution of normal tissue stem cells and cancer stem cells to tumorigenesis.The two papers referred to are these [neither are publicly accessible]:
1) Crypt stem cells as the cells-of-origin of intestinal cancer by Nick Barker and 9 co-authors, including Hans Clevers, Nature 2008(Dec 17) [Epub ahead of print][PubMed Citation].
2) Prominin 1 marks intestinal stem cells that are susceptible to neoplastic transformation by Liqin Zhu and 9 co-authors, including Richard Gilbertson, Nature 2008(Dec 17) [Epub ahead of print][PubMed Citation].
See also this blog post: Two articles linking normal intestinal SC to CSC, December 18, 2008.