C-MYC, C-FOS, AND C-MYB GENE-EXPRESSION IN HUMAN PITUITARY-ADENOMAS

The possible roles of certain oncogenes in the development of pituitar y tumors has not been investigated. We have examined the expression of c-myc, c-fos, and c-myb in a number of human pituitary tumors by ribo nuclease protection assays, as these oncogenes have been implicated to have roles in the pathogenesis of other human tumors (12, 13, 15, 16) . In several tumors examined (9 of 30) c-myc was expressed at levels 4 -9 times greater than the level detected in normal postmortem pituitar y. Although a larger percentage of negative immunohistochemical-staini ng tumors overexpressed c-myc, c-myc overexpression was not limited to this group of tumors. c-Fos was overexpressed in 1 of 30 tumors exami ned at a level 5.8-fold higher than that detected in normal postmortem pituitary. This tumor stained positive for ACTH by immunohistochemist ry and was considered highly aggressive, demonstrating invasion beyond the sella turcica; however, when other ACTH-staining and invasive pit uitary tumors were examined, no abnormality in the expression of c-fos was detected. In 30 tumors, c-myb was expressed at approximately the same level as that detected in normal postmortem pituitary. We conclud e that c-myc is overexpressed in a subgroup of pituitary tumors and th at this overexpression occurs broadly among the different groups of im munohistochemical-staining tumors. c-Fos overexpression appears to be much less common in pituitary tumors and does not necessarily correlat e with the ability of the tumor to become invasive. c-Myb does not app ear to have a role in the pathogenesis of pituitary tumors.