Loss of E-cadherin and cytoplasmic-nuclear expression of beta-catenin are the most useful immunoprofiles in the diagnosis of solid-pseudopapillary neoplasm of the pancreas.

Solid-pseudopapillary neoplasm of the pancreas occurs preferentially in young women and has a favorable prognosis. Differentiation of solid-pseudopapillary neoplasm from pancreatic endocrine neoplasm or adenocarcinoma can be difficult in the small biopsy specimen because they share common morphological features and immunoprofiles. Alterations of adenomatous polyposis coli (APC)/beta-catenin pathway have been identified as a genetic event contributing to the development of solid-pseudopapillary neoplasm. In the present study, to establish the diagnostic utility of beta-catenin and E-cadherin as markers for solid-pseudopapillary neoplasm, we performed immunohistochemical staining in 4 core biopsy specimens diagnosed as solid-pseudopapillary neoplasm and in tissue microarray blocks that contained histologically confirmed samples of 302 cases of adenocarcinoma, 56 cases of pancreatic endocrine neoplasm, and 50 cases of solid-pseudopapillary neoplasm. We compared the immunohistochemical results for beta-catenin and E-cadherin with those for known markers. Of the solid-pseudopapillary neoplasm cases, 51 (94.4%) were positive for nuclear beta-catenin, 45 (83.3%) were positive for CD10, 30 (55.5%) were positive for CD56, 15 (27.8%) were positive for synaptophysin, 3 (5.6%) were positive for cytokeratin (CK), and none was positive for E-cadherin and chromogranin. Of the adenocarcinoma cases, all were positive for CK, 300 (99.3%) were positive for E-cadherin, 30 (9.9%) were positive for CD10, 2 (0.7%) were positive for synaptophysin, 1 (0.3%) was positive for CD56, and none was positive for chromogranin and nuclear expression of beta-catenin. Of the pancreatic endocrine neoplasm cases, 54 (96.4%) were positive for synaptophysin and E-cadherin, 50 (89.3%) were positive for chromogranin, 26 (46.4%) were positive for CK, 15 (26.8%) were positive for CD56, 6 (10.7%) were positive for CD10, and none was positive for nuclear expression of beta-catenin. In conclusion, nuclear expression of beta-catenin and loss of E-cadherin can be used in the definite diagnosis of solid-pseudopapillary neoplasm on small biopsy specimens. CD10 immunopositivity should be carefully interpreted in the diagnosis of solid-pseudopapillary neoplasm because pancreatic adenocarcinoma or pancreatic endocrine neoplasm can also stain for CD10.