Fine structural evidence for hormone secretion by a human thymic tumour.

An epidermoid type of thymoma from an asymptomatic 39-year-old male subject is described. Electron microscopy demonstrated endocrine type secretory granules within the tumour cells, and a minority of these granules resembled normal human pancreatic alpha cell granules. Fine structural evidence for endocrine secretory activity in a primary thymic tumour has not been previously described. There are few fine structural reports of primary thymic tumours in man and to our knowledge these do not include certain features of the case described here.