Background:Pituitary adenoma and neuronal components may coexist in the sellar region, but discussion of the histogenesis of the neuronal component has been mainly based on the morphological similarity with the adenomatous component using immunohistochemical and ultrastructural methods. Neuronal differentiation within pituitary adenoma may be a metaplastic process, but no clear supporting evidence has been obtained. To investigate the monoclonality or polyclonality of the mixed lesion by the X-chromosome inactivation method.Case Report:Tumor specimens from a 55-year-old acromegalic woman were subjected to histopathological study and clonal analysis. Histological examination found varying proportions of adenoma cells and neuronal component in the specimens. Light and electron microscopy revealed cells with transitional morphology between adenoma cells and neurons. However, the X-chromosome inactivation method demonstrated monoclonality of both adenoma and neuron-like cells.Conclusions:Clonal analysis of the mixed lesion demonstrated that all tumor cells originated from a single cell.

Keywords: Adenoma - genetics, Adenoma - pathology, Adenoma - secretion, Chromosomes, Human, X - genetics, Human Growth Hormone - secretion, Pituitary Neoplasms - genetics, Pituitary Neoplasms - pathology, Pituitary Neoplasms - secretion