Answer: Well-differentiated pancreatic endocrine neoplasm

Histology: see below

Discussion: Well Differentiated Pancreatic Endocrine Neoplasms is the current terminology replacing the islet cell tumor terminology for pancreatic endocrine neoplasms that are more than 0.5 cm in size and demonstrate a relatively low mitotic activity of less than 10/10HPF. Tumors less than 0.5 cm in diameters are termed microadenomas. The minority of Pancreatic Endocrine Neoplasms occurring in the familial setting of MEN1, and rarely vHL syndrome, are usually multiple and associated with microadenomas.

Negative prognostic factors in Well Differentiated Pancreatic Endocrine Neoplasms include tumor size (5cm or more), extra-pancreatic extension, presence of necrosis, high mitotic rate, large vessel invasion and metastasis. Histologically, the differential diagnosis of Well Differentiated Pancreatic Endocrine Neoplasms may at times include solid pseudopapillary neoplasm. The latter differential is further made difficult by the fact that both tumors express CD56 and synaptophysin. Attention to typical features of solid pseudopapillary neoplasm including the presence of intracyroplasmic large hyaline globule and nuclear grooves together with their positive expression of CD10, abnormal nuclear staining for B-catenin and negative staining for chromogranin would help resolve difficult cases.