Immunohistochemical studies of human FSH producing pituitary adenomas

Ten FSH producing pituitary adenomas were studied immunohistochemically. 9 cases were in males, and 7 showed elevated serum FSH levels. Immunohistochemically, all cases showed the presence of alpha-subunit and FSH-beta subunits in many tumour cells. These two subunits were frequently colocalized in the same cells. However, the expression of LH-beta subunit was extremely low (1 of 10 cases exhibiting occasional LH-beta positive tumour cells), although it has been reported that FSH-beta and LH-beta subunits are colocalized in the same cells of the normal adult pituitary gland. Immunoelectron microscopically, alpha-subunits and FSH-beta were present in the secretory granules and suggested the co-release of subunits or secretion of combined form of FSH. In 7 cases, TSH-beta was positive, and in some cases, TSH-beta was colocalized in the same tumour cells which contained alpha-subunit and FSH-beta subunit. A few cases also demonstrated immunoreactivity for PRL and ACTH. Our immunohistochemical studies suggest that FSH adenomas are multihormonal and that there is abnormal gene expression in FSH cells with loss of LH-beta appearance and co-expression of TSH-beta.