Although Kras/KRAS mutation promotes serrated and hyperplastic morphologic features in colon epithelium, it is not able to initiate adenoma development, perhaps in part because activated Kras/KRAS signaling does not increase the number of presumptive stem cells in affected crypts.
Feng, Y., Bommer, G., Zhao, J., Green, M., Sands, E., Zhai, Y., Brown, K., Burberry, A., Cho, K. R., & Fearon, E. R. (2011). Mutant KRAS promotes hyperplasia and alters differentiation in the colon epithelium but does not expand the presumptive stem cell pool. Gastroenterology, 141(3), 1003-1013. https://doi.org/10.1053/j.gastro.2011.05.007 (Original work published 2011)