β-catenin mutation in ovarian solid pseudopapillary neoplasm.

Primaly solid pseudopapillary neoplasm (SPN) of the ovary is a rare tumor; recently 6 cases have been reported. Its pathogenesis, however, remains largely unclear. We report an additional case of primary ovarian SPN of an 18-year-old girl. The aim of this study is to define the difference between pancreatic and ovarian SPN by histological and molecular examination. Microscopically the tumor predominantly showed a solid pattern and focally a pseudopapillary pattern. The tumor cells showed two patterns of abundant eosinophilic cytoplasm and intracytoplasmic vacuoles. Immunohistochemistry of the tumor was positive for β-catenin (nuclear and cytoplasmic reactivity), α1-antitrypsin, vimentin, CD56, synaptophysin (focal weak), CD10. Mutation analyses revealed a point mutation, c.110C >T, in exon 3 of the the β-catenin gene (CTNNB1), which causes the replacement of serine with phenylalanine at codon 37. A Ser37 point mutation is known to be one of the oncogenic somatic mutations in pancreatic SPN and the major oncogenic β-catenin mutation. Ovarian SPN of our case was similar to pancreatic SPN histologicaly and had the same genomic characteristics. We expected that both ovarian and pancreatic SPNs shared the same oncogenesis related to Wnt/β-catenin pathway for tumorgenesis.