Clear-cell variant of solid-pseudopapillary neoplasm of the pancreas: a case report and review of the literature.

Solid-pseudopapillary neoplasm (SPN) of the pancreas is a rare neoplasm reported to have a favourable prognosis because of its slow-growing behaviour. Ignored and misdiagnosed in the past, SPN has recently been increasingly studied. Its clear cell variant creates challenges in distinction from other clear cell tumours in the pancreas. We report a 31-year-old Cambodian woman who presented with abdominal pain and a palpable epigastric mass. Exploratory laparotomy revealed a 5.2 cm well-demarcated tumour in the head of the pancreas, which was treated with Whipple procedure. Microscopically, the tumour showed an extensive solid growth pattern consisting of cells with abundant clear cytoplasm, and papillary areas containing cells with eosinophilic cytoplasm, indicating a clear-cell solid-papillary neoplasm. Perineural and duodenal wall invasion was present. The tumour cells were immunonegative for chromogranin-A and synaptophysin but positive for CD56, cyclin D1, CD10, vimentin, and progesterone receptor. They showed strong nuclear and cytoplasmic expression and reduced membranous expression of beta-catenin protein. In the pseudopapillary area, they showed nuclear E-cadherin localization and absence of membranous staining. The patient was well without local recurrence or metastasis at one year follow-up. Difficulties are recognized in differentiating clear-cell SPN from "sugar" tumours, metastatic renal cell carcinoma, clear-cell variant of pancreatic endocrine neoplasm and ductal adenocarcinoma. When facing such difficulties, nuclear and cytoplamic beta-catenin, nuclear E-cadherin expressions and absence of membranous E-cadherin staining are useful in differentiating clear-cell SPN from other clear cell tumours in the pancreas. Although a rare neoplasm, it is important to recognize this entity for appropriate management.