Significance of positive and inhibitory regulators in the TGF-β signaling pathway in colorectal cancers.

Inactivation of genes in the transforming growth factor (TGF)-β/SMAD signaling pathway is a well-known step for the progression of colorectal cancers (CRCs). Genetic mutations can occur in the precursors, and the combined prevalence of SMAD4, SMAD2, and SMAD3 mutations was seen in up to 50% of CRCs. High levels of serum TGF-β1 were reported in patients with CRC and were associated with poor clinical outcome.