KRAS and tubulovillous adenoma: Furthermore, a recent systematic review suggested tubulovillous adenomas with serrated features to be precursors of KRAS mutant tumors.44 Tsai et al. evaluated the pathological and molecular features of 60 TSAs with cytologic dysplasia and/or invasive carcinoma, and shown that tubulovillous adenoma with serrated features had higher frequencies of KRAS mutations than TSAs with serrated dysplasia.44,45 Potential precursor lesions assigned to the CMSs based on the above research results are shown in Figure 2.