In order to search for candidate genes related to pituitary adenoma aggressiveness, the present investigation was intended to compare the mRNA expression profile from a pool of four nonfunctional pituitary adenomas (NFPA) with a spinal cord metastasis of a nonfunctional pituitary carcinoma (MNFPC). The metallothionein isoform 3 (MT3) gene was differentially expressed in nonfunctional adenomas in comparison to the metastasis of nonfunctional carcinoma. A microarray dataset comprising 19,881 probes was employed for comparing expression profiles of a spinal cord metastasis of a nonfunctional pituitary carcinoma with a pool of four nonfunctional pituitary adenomas. RT-qPCR confirmed the microarray findings and was used to investigate MT3 mRNA gene expression in tumor samples of a series of 52 different pituitary adenoma subtypes comprising 10 corticotropin (ACTH)-producing, 18 growth hormone (GH)-producing, 8 prolactin (PRL)-producing, and 16 nonfunctional adenomas. Microarray data analysis by GeneSifter program unveiled Gene Ontology terms related to zinc ion-binding activity closely related to MT3 function. MT3 mRNA expression was statistically significantly higher in ACTH-producing pituitary adenomas and in nonfunctional pituitary adenomas in comparison to the other pituitary adenoma subtypes. The more abundant expression of this gene in ACTH-producing pituitary adenomas suggests that MT3 could be related to distinct pituitary cell lineage regulating the activity of some transcription factor of importance in hormone production and/or secretion.