Metastasis-Specific APC Alteration and Nuclear β-Catenin Accumulation in IPMN-Associated Pancreatic Ductal Adenocarcinoma: Genomic Analysis of Matched Precursor, Carcinoma, and Liver Metastasis—A Case Report

Background: The molecular changes associated with the progression of intraductal papillary mucinous neoplasm (IPMN) to pancreatic ductal adenocarcinoma (PDAC) and distant metastasis remain incompletely understood. Case Presentation: A man in his late 70s underwent pancreaticoduodenectomy and partial hepatectomy for a pancreatic head tumor with synchronous liver metastasis. Histology showed a 4.5 cm moderately differentiated PDAC arising in an IPMN with high-grade dysplasia (pT3N1M1). Genomic analysis of the IPMN, PDAC, and liver metastasis identified KRAS p.G12D, CDKN2A deletion, and GNAS p.R201H in the IPMN; additional SMAD4 p.R361C in the PDAC; and KRAS p.G12D, CDKN2A deletion, SMAD4 p.R361C, and APC p.R1450Ter in the liver metastasis. The APC alteration was confirmed by targeted sequencing and was accompanied by loss of heterozygosity at the APC locus. β-Catenin showed membranous expression in the IPMN and PDAC, but nuclear accumulation in the liver metastasis. Discussion: The shared KRAS, CDKN2A, and SMAD4 alterations support a common clonal origin of the PDAC and metastatic tumors. The absence of a detectable GNAS alteration in the liver metastasis and the presence of a metastasis-specific APC alteration are compatible with, but do not prove, branching evolution and selection of a metastatic subclone. Conclusions: This case shows a metastasis-specific heterozygous APC truncating alteration with loss of heterozygosity, accompanied by nuclear β-catenin accumulation, in an IPMN-associated PDAC.