Pituitary adenomas are benign tumors of the brain, with a relatively high prevalence in the general population, being responsible for 14.4-16.7% from all brain tumors. These tumors, although benign, have a local invasive behavior in approximately 35% of the cases. The aim of this study was to identify the differences in expression of molecular markers between primary and relapsed pituitary adenomas (as an aggressiveness indicator), as well between secreting and non-secreting pituitary adenomas. Tumor fragments were collected from 51 patients with invasive pituitary adenomas. Of these, 10 cases were operated a second time due to tumor recurrence. The tumor fragments were retrieved from the archives of the Department of Pathology, Emergency County Hospital, Cluj-Napoca, Romania. Immunohistochemical staining was performed for nine markers on 51 invasive pituitary adenomas: Ki-67, β-catenin, E-cadherin, Bcl-2, galectin-3, p53, p27, CD117, and CD44. We compared the expression differences between two groups: the first one including primary and relapsed invasive pituitary adenomas, and another one including prolactin (PRL)-secreting and non-secreting invasive pituitary adenomas. Ki-67, p53 and Bcl-2 expressions were found significant in the PRL-secreting group. CD44 immunostaining was significant only in relapsed invasive pituitary adenomas. For the β-catenin, E-cadherin, galectin-3, p27 and CD117 expression levels were not registered statistically significant differences between our groups. Our study is the first one to report a statistically significant difference between the expression of CD44 in primary and relapsed invasive pituitary adenomas and it could be used as a negative impact prognostic marker.