Expression pattern of claudins 5 and 7 distinguishes solid-pseudopapillary from pancreatoblastoma, acinar cell and endocrine tumors of the pancreas.
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.