SMAD4/DPC4 nuclear loss on immunohistochemistry can support an interpretation of pancreatic ductal adenocarcinoma even when there is signet ring cell morphology (this example is more typical).
Simbolo M, et al. Clinical and Genomic Characterization of Pancreatic Ductal Adenocarcinoma with Signet-Ring/Poorly Cohesive Cells. Mod Pathol. 2023 Sep;36(9):100251. PMID: 37355152.