Solid serous adenoma of the pancreas. The solid variant of serous cystadenoma?

Serous cystadenomas of the pancreas are uncommon benign neoplasms that occur most frequently in elderly females. Characteristically, the tumors have a spongy gross appearance and are composed of innumerable cysts lined by flat, cuboidal, and polygonal cells with clear to pale eosinophilic cytoplasm and round, hyperchromatic central nuclei. Macrocystic variants with an oligolocular gross appearance have also been described. In this report we describe a solid pancreatic neoplasm arising in a 70-year-old woman who remains well 5 years after a distal pancreatectomy. The well-circumscribed tumor measured 4.0 cm in maximal diameter and was formed by clear to pale polygonal to cuboidal cells arranged in nests, sheets, and trabeculae separated by thick fibrous bands. Although small acini with glandular spaces were present within the nests, cystic spaces were absent. Periodic acid-Schiff (PAS) and PAS-dismutase (PAS-D) stains revealed a large amount of cytoplasmic glycogen. The tumor cells were immunoreactive for CAM 5.2, epithelial membrane antigen, and neuron-specific enolase. The cytologic, histochemical, and immunohistochemical features of the tumor were indistinguishable from those of serous cystadenomas; therefore, we believe this solid serous adenoma represents a solid variant of serous cystadenoma. Recognition of this lesion is important because the vast majority of solid tumors in the pancreas are malignant. The differential diagnosis includes the rare primary clear-cell "sugar" tumor of the pancreas, clear cell carcinoma, clear cell islet cell tumor, and metastatic renal cell carcinoma.