PTEN and colorectal carcinoma: MSI-H CRC is characterized by a distinct clinical behavior and has better prognosis than their MSS counterparts.[21] PTEN is a tumor suppressor gene, inactivation of which causes deregulation of the PI3K pathway and loss of which has been associated with aggressive CRC and predicts nonresponse to cetuximab.[22] TS is the target enzyme for fluorouracil.