SMAD4 encodes a tumor suppressor and transcription factor that is a downstream effector in the TGF-ss signal transduction pathway. Germline mutations in SMAD4 have been associated with juvenile polyposis syndrome. SMAD4 is mutated in one third of colorectal cancer and half of pancreatic tumors. Genetic alterations in SMAD4 have been identified in 33% of pancreatic adenocarcinomas. SMAD4 inactivation by allelic deletion or mutation mainly occurs in late stage pancreatic ductal adenocarcinoma and is associated with poorer prognosis. SMAD4 D351G lies at a hotspot residue within the MH2 domain of the Smad4 protein (UniProt.org). D351G has been identified in sequencing studies, but has not been biochemically characterized and therefore, its effect on Smad4 protein function is unknown. The SMAD4 D351H variant has been described in human colorectal cancer cell lines and reported as likely oncogenic, suggesting that the D351G variant is also likely to be oncogenic. SMAD4 loss has been found to increase resistance to the chemotherapeutic agent 5'-fluorouracil.