Missense mutations in the kinase domain (KD) of TGF-beta receptor II (TGFBR2) are found in ~20% of microsatellite stable (MSS) colon cancers and make affected tumors resistant to TGF-beta (TGFB1)-mediated growth inhibition (Grady et al. 1999). While both alleles of TGFBR2 are affected by inactivating mutations in MSS colorectal cancer (Grady et al. 1999), a study of MSS esophageal carcinoma indicates that TGFBR2 KD mutations may function in a dominant-negative way (Tanaka et al. 2000). KD mutations in TGFBR2 are rarely reported in microsatellite instable (MSI) colorectal cancer (Parsons et al. 1995, Takenoshita et al. 1997).