TGFBR2 and colorectal carcinoma: In human CRC, TGFBR2 mutations are frequently observed as a 10-bp poly-adenine repeat in exon 3, called the big adenine tract (BAT-RII); the BAT-RII is a microsatellite sequence prone to replication errors, resulting in insertion or deletion of one or two adenines, thereby introducing truncated, nonfunctional TGFBR2 protein.