Expression of Wnt Target Genes in Solid Pseudopapillary Tumor of the Pancreas

Abstract

Solid pseudopapillary tumor (SPT) of the pancreas is very rare. This study was performed to analyze the expression of Wnt signal target genes (matrix metalloproteinase-7 [MMP-7], cyclin-D1, and c-myc) and Ki-67 in resected SPTs to determine their clinicopathologic characteristics according to their expression. From January 1995 to December 2005, 23 patients underwent pancreatic resections for SPT of the pancreas. Among 23 formalin-fixed, paraffin-embedded tissues, 12 were evaluated as a pilot study. Immunohistochemistry was performed using various detection and antigen retrieval methods to detect MMP-7, cyclin-D1, c-myc, and Ki-67. The expression of Wnt target genes was correlated with clinicopathologic features of the patients. Solid pseudopapillary tumors of the pancreas always showed cytoplasmic/nuclear accumulation of [beta]-catenin, frequent expression of cyclin-D1, and low proliferation index. MMP-7, cyclin-D1, c-myc, and Ki-67 were not correlated with microscopic features suggesting malignant potential (P > 0.05). Tumor size was closely related to microscopic features of malignant potential and apparently has an inverse relationship with the expression of cyclin-D1 and Ki-67 (P < 0.05). Low proliferative index and associated MMP-7 expression may cause an unpredictable clinical course in this tumor. Subtle changes in the intracellular environment, not pathologic (morphologic) changes, may elucidate the unpredictable clinical course of this tumor.