Abstract
Solid-pseudopapillary neoplasms are rare, but are distinctive pancreatic tumors of low-malignant potential. While the histogenesis of these tumors is unclear, they are often associated with gain-of-function mutations in the catenin (cadherin-associated protein), beta 1 (88 kDa), or CTNNB1 gene, resulting in nuclear accumulation of CTNNB1. CTNNB1 is a central component of the Wnt signaling pathway and mediates gene expression through the lymphoid enhancer-binding factor 1 (LEF1) /T-cell factor transcription complex. Although LEF1 has a pivotal role in the transactivation of Wnt/CTNNB1 responsive genes, the status of LEF1 in solid-pseudopapillary neoplasms and other pancreatic tumors has not been examined. We analyzed both LEF1 and CTNNB1 in a large cohort of pancreatic tumors (n=155). In all cases of solid-pseudopapillary neoplasms including surgical resections (n=27) and cytologic samples (n=8) had strong and diffuse nuclear labeling for both LEF1 and CTNNB1. The surrounding uninvolved pancreatic parenchyma was devoid of any LEF1 staining. All resection and cytologic specimens from well-differentiated pancreatic neuroendocrine tumors (n=44; n=29, respectively), high-grade pancreatic neuroendocrine carcinomas (n=2; n=1), pancreatic ductal adenocarcinomas (n=25; n=12), and acinar cell carcinomas (n=9; n=2) studied were negative for both nuclear LEF1 and CTNNB1. However, nuclear LEF1 and CTNNB1 were detected in all four resected pancreatoblastomas (no cytologic specimens were available for immunolabeling), but primarily centered around and within squamoid corpuscles. In summary, abnormal CTNNB1 accumulation was accompanied by nuclear LEF1 overexpression in both solid-pseudopapillary neoplasms and pancreatoblastomas. But, in contrast to pancreatoblastomas, a diffuse, nuclear labeling was observed in solid-pseudopapillary neoplasms and further implicates the CTNNB1/LEF1 transcriptional complex in the development of solid-pseudopapillary neoplasms. In addition, as part of an immunohistochemical panel, LEF1 can be a useful ancillary stain in the diagnosis of solid-pseudopapillary neoplasms.