Solid pseudopapillary neoplasm collides with a well-differentiated pancreatic endocrine neoplasm in an adult man: case report and review of histogenesis.

OBJECTIVES: Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare, clinicopathologically distinct neoplasm with a tendency to affect young women. The histogenesis of SPN is not well defined. Pancreatic endocrine neoplasms (PENs) are also uncommon tumors of the pancreas.
METHODS: Our comprehensive review of the literature did not yield any reported cases of collision tumors of the above two neoplasms. We report a case of such a collision tumor in a 45-year-old man.
RESULTS: This tumor was an incidental finding on computed tomography, followed by fine-needle aspiration confirmation of a tumor that was initially diagnosed as an SPN only. A histologic examination of a 2.1-cm mass following distal pancreatectomy revealed a 0.7-cm PEN partly engulfed by an SPN. The tumors showed different morphologic and immunohistochemical features, confirming the presence of a collision tumor.
CONCLUSIONS: A comparative analysis of immunoprofiles of these tumors yielded interesting findings, enabling us to postulate that SPNs may originate from a multipotential primordial cell that may follow different differentiation pathways, such as endocrine, epithelial, and acinar. The ultrastructures and immunophenotypic characteristics appear to support this hypothesis. Copyright© by the American Society for Clinical Pathology.