TSH-secreting
pituitary adenomas are rare. The transcriptional expression (messenger
ribonucleic acids: mRNAs) of
TSH beta, GH, and PRL in five patients with TSH-secreting
pituitary adenoma was studied by the in situ hybridization (ISH) method in order to elucidate their multiple
hormone production. These patients showed inappropriately elevated serum TSH and alpha-subunit levels as well as pituitary mass lesions. The tissues from
pituitary adenomas were obtained at the time of transsphenoidal surgery and revealed immunohistochemically the expression of alpha-subunit and
TSH beta in all patients. Four
adenomas were immunohistochemically associated with GH or PRL localization. The presence of pituitary-specific transcriptional factor Pit-1 was demonstrated in all
adenomas in the nuclei of many cells. By ISH, signals for
TSH beta mRNA were present in all five cases in many
adenoma cells. Expression of GH
mRNA and PRL
mRNA were detected not only in four
adenomas in which both hormonal products were immunolocalized but also in one
adenoma that was immunohistochemically negative for GH and PRL. Combined staining by ISH and immunohistochemistry revealed the expression of GH
mRNA and PRL
mRNA in
TSH beta-immunoreactive cells. Our findings indicate that TSH-secreting
adenomas are multihormone-producing and could arise from precursor or stem cells rather than from differentiated TSH-secreting cells. It is suggested that ISH combined with immunohistochemistry may provide additional detailed information concerning the multidirectional histogenesis of this rare type of
adenoma.