Clinical, biochemical and immunoelectron microscopical evidence of dual hormone production in a mammosomatotroph cell adenoma

This paper reports the occurrence of a rare, yet distinct pituitary adenoma which was surgically removed from a 42‐year‐old male with both clinical and biochemical evidence of acromegaly and mild hyperprolactinaemia. The monomorphic adenoma consisted of mature cells which were ultrastructurally indistinguishable from those of a prolactinoma. Electron immunocytochemistry, including a series of double‐labelling techniques using selected colloidal gold particles as markers, indicated the presence of a pituitary adenoma in which the cells were capable of simultaneously producing growth hormone and prolactin and packaging them within the same secretory granule. This is thought to represent a mammosomatotroph cell adenoma.