Solid-pseudopapillary
tumor (SPT) of the pancreas is characterized by a discohesive appearance of the neoplastic cells. This has been linked to the displacement of
E-cadherin and
beta-catenin from their normal membrane location, which prevents adherens junctions to form. The nuclear localization of
beta-catenin is also a feature of SPT that helps in differential diagnosis. This latter includes pancreatic endocrine
tumor (PET) as SPT may show neuroendocrine differentiation, and pancreatic
acinar cell carcinoma (ACC) and
pancreatoblastoma (PB) that may often show nuclear
beta-catenin staining. However, the role of additional cell-cell adhesion systems remains to be elucidated in SPT, particularly that of
claudins that are essential components of tight junctions showing modulated expression in diverse
tumor types. We studied 20 SPT, 20 nonfunctioning PET, 7 ACC, 2 PB, and their matched normal pancreas for the immunohistochemical expression of
claudin family members 1, 2, 3, 4, 5, and 7,
beta-catenin and
E-cadherin. All SPT showed intense membrane
claudin 5 and cytoplasmic
claudin 2 staining, lack of
claudins 3 and 4, and positive cytoplasmic
claudins 1 and 7 in few cases. Conversely, PET, ACC, and PB showed strong membrane expression of
claudin 7 and lack of
claudin 5, whereas
claudins 1, 2, 3, and 4 showed variable expression among samples. All SPT showed nuclear
beta-catenin and lack of
E-cadherin membrane staining, whereas PET, ACC, and PB only showed nuclear
beta-catenin in 1, 2, and 2 cases, respectively. SPT shows a peculiar
claudin expression profile and the highly specific pattern of
claudins 5 and 7 differentiates SPT from PET, ACC, and PB.