SMAD4 and colorectal cancer: Having identified TGF-β1-BMP-Smad4 pathway dependency of Id1low and Spp1high gene expression, and Pak3high expressing cell enrichment in primary caecal intestinal adenoma, we next explored whether any of these functional gene expression biomarkers are also present in human colorectal cancer (Fig. 5, Fig. 6, Supplementary Table 5).