Clinicopathological analysis of β-catenin and Axin-1 in solid pseudopapillary neoplasms of the pancreas.

Background: Solid pseudopapillary neoplasm (SPN) is a distinct pancreatic neoplasm and has characteristic, aberrant nuclear expression of β-catenin in most cases. However, alterations in components of the Wnt pathway, other than the β-catenin (CTNNB1) gene mutation, have not been identified. In this study, we investigated the status of Axin-1, the spectrum of mutations in the CTNNB1 gene, and the clinicopathological features of SPNs.

Methods: We collected 27 SPNs from 25 patients. A tissue microarray was constructed to perform immunohistochemistry for β-catenin, E-cadherin, and Axin-1. The CTNNB1 and AXIN1 gene mutations were analyzed by DNA sequencing. Finally, the clinicopathological features of SPNs were analyzed for association with the CTNNB1 mutations and the Axin-1 alterations.

Results: All 27 SPNs expressed nuclear immunoreactivity of β-catenin and exhibited a lack of membranous decoration of E-cadherin. All SPNs harbored CTNNB1 gene mutations. No alterations were present in the AXIN1 gene, and the immunohistochemical analysis revealed weak or absent reactivity of Axin-1 in the cytosol. All cases with a codon-37 CTNNB1 mutation had weak Axin-1 immunoreactivity in the cytoplasm (P = 0.018). No other significant correlation was found between clinicopathological parameters, CTNNB1 mutations, and Axin-1 alterations.

Conclusions: Nuclear β-catenin immunoexpression is characteristic for SPNs and corresponds to the CTNNB1 mutation. The Wnt pathway is involved in the tumorigenesis of SPNs, primarily through the alteration of β-catenin. Despite the absence of any identifiable genetic mutation, a low level of Axin-1 in the cytoplasm might contribute to the aberrant distribution of β-catenin in SPNs.