Heterozygous or homozygous deletion of SMAD4 was first discovered in pancreatic ductal adenocarcinoma (39) and later detected in various types of cancers, such as colorectal cancer (40), cholangiocarcinoma (41), gastric cancer (42), and prostate cancer (43), although with lower frequencies to some extent. This evidence concerns the gene SMAD4 and pancreatic ductal adenocarcinoma.