In primary pancreatic ductal adenocarcinoma, CK 19 showed diffuse cytoplasmic positivity in 23 of 25 cases, CA 19-9 showed apical cytoplasmic staining in all 25 cases, and SMAD4 showed nuclear staining in 20 of 25 cases. The gene discussed is SMAD4; the disease is pancreatic ductal adenocarcinoma.