Distinct Genomic Profiles of Two Small Malignant Lesions Associated With an Intraductal Papillary Mucinous Neoplasm Co-occurring in a Patient.

Intraductal papillary mucinous neoplasm of the pancreas (IPMN) is characterized by cystic dilatation of the pancreatic duct system, intraductal papillary growth, and excessive mucin secretion. Although IPMN is basically a benign disease and surgical resection is not necessary, it has the potential to develop into pancreatic cancer. We recently encountered a rare case of synchronous development of two different types of malignant lesions in the pancreas associated with IPMN derived from different clones. A 74-year-old Japanese woman developed a cystic lesion in her pancreatic tail. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) was performed on two low echoic lesions in the pancreatic tail (10 mm) and body (10 mm), which were then diagnosed as malignancies. After the surgically resected pancreas was carefully examined, in addition to the tail (10 mm) and body (10 mm) tumors, an intraductal papillary mucinous adenoma (IPMA) was observed, which was continuous to the tail tumor and extending toward the body of the pancreas but not contiguous to the body tumor. Genomic analysis using targeted sequencing revealed that the malignant lesion in the pancreatic tail and two sections of adjacent IPMA lesions in the pancreatic duct were almost identical. KRAS G12D, RNF43 G29fs, PBRM1 P1471R, and PIK3CA I1058L were shared, whereas only KRAS G12D was shared between the malignant lesion in the pancreatic body and others. Multiple pancreatic cancers may occur simultaneously and/or metachronously in the context of genomic alterations in IPMN.