- In addition to the classical anterior pituitary hormones, many human pituitary adenomas express hormone genes ectopically. Expression of glycoprotein hormone alpha-subunit and, less commonly, free luteinizing hormone beta (LH-beta) or follicle-stimulating hormone beta is characteristic of endocrinologically inactive adenomas, a subgroup thought to be derived predominantly from the gonadotroph line. Thyrotrophin beta expression in these tumours is unusual, and specific chorionic gonadotrophin beta (CG-beta) expression, identified using oligonucleotide probes that reliably distinguish LH-beta and CG-beta in situ, is not well described. Using in situ hybridization histochemistry with a CG-beta transcript-specific oligonucleotide probe and a non-specific LH/CG-beta oligonucleotide and riboprobe, we have demonstrated specific CG-beta expression in two of 35 random pituitary adenomas; LH-beta expression occurred in a further eight adenomas. Unlike prolactin, growth hormone and proopiomelanocortin, which are transcribed in the vast majority of cells in their respective hormone-positive tumour subtypes, the pattern of LH/CG-beta was typically a scattering of single or small clusters of hormone-positive cells in a predominantly LH/CG-beta-negative tumour. Finally, although bona fide CG-beta expression in human pituitary adenomas does occur, it is only at an incidence similar to that described for carcinomas of other tissues.