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

OBJECTIVES: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.