Serous oligocystic adenoma of the pancreas: a clinicopathological and immunohistochemical study of three cases with ultrastructural findings.

Aims: Serous oligocystic adenoma of the pancreas is an uncommon benign neoplasm and is a recently described entity. To date, there are 19 adult cases of this tumour. We report three additional cases, two with macrocystic and one with unilocular types. We describe their clinicopathological, immunohistochemical and ultrastructural findings and review the world's literature.

Methods: For a 10-year period, we reviewed all benign cystic lesions of the pancreas with emphasis on serous oligocystic adenoma. We characterised serous oligocystic adenoma as an ill-demarcated or encapsulated mass, composed largely or exclusively of macrocysts (cysts measuring 20mm or more) but few in number (oligolocular). Grossly, it may contain only a single cyst (unilocular) of any size with a few satellite cysts observed on histological examination. Special stains and immunohistochemistry as well as electron microscopy were performed on three and two cases of serous oligocystic adenoma, respectively.

Results: Between 1990 and 2000, we collected 26 benign cystic lesions of the pancreas, three of which were serous oligocystic adenomas (two with macrocystic and one with unilocular types). Many of the cells lining the cysts showed PAS positivity. There was negative staining for PAS with diastase digestion, Alcian blue and mucicarmine. All cases showed positive staining for CAM5.2, AE1/AE3, EMA and CK7. The proliferation index marker was low. There was negative staining for CK20, insulin, glucagon, somatostatin, synaptophysin, chromogranin A, CEA and p53. Ultrastructural studies on two cases revealed similar findings. The single row of uniform epithelial cells lining the cysts was composed of simple cuboidal to flat cells which rested on a thin basal lamina. Their nuclei were round to ovoid. Glycogen granules were identified in the cytoplasm. Short microvilli emerged from the epithelial apical surface. Adjacent tumour cells were connected by microfilaments.

Conclusions: Serous oligocystic adenomas of the pancreas are uncommon benign tumours. Prior to this study, 19 adults with these lesions were reported in the world's literature. No correct pre-operative diagnosis was carried out on all 22 cases. The 20 patients with follow-up ranging from 2 months to 5 years did not show tumour recurrence or malignant transformation.