Pituitary tumor-transforming gene (PTTG) is also known to induce angiogenesis during pituitary tumorigenesis. It has not been clarified whether PTTG functions as a cytoplasmic or a nuclear protein. Pituitary tumor-transforming gene-1 is usually expressed in most pituitary tumors, and little is known about phosphatase and tensin homologue (PTEN). In our knowledge, it has not been studied in pituitary tumors. The aim of this study was to determine the correlation between proliferating cell nuclear antigen (PCNA) labeling index (LI), PTEN, and PTTG-1 immunoexpression in pituitary adenomas. Forty-five pituitary adenomas were included-46.7% were males and 53.7% were females. The mean age was 43.18 +/- 9.42 years (27-70 years). For functional pituitary adenoma (PA), it was 41.92 +/- 6.63, and for nonfunctional pituitary adenomas, it was 44.62 +/- 11.85 (P = .003). Proliferating cell nuclear antigen LI range was 19.42 +/- 5.49; in functional pituitary adenomas, it was 41.92 +/- 6.63, and in nonfunctional adenomas, it was 44.62 +/- 11.85 (P = .081). The PTEN immunoreaction was positive-weak in 21 (47%), moderate in 19 (42%), and strong in 5 (11%; P = .000). The PTTG-1 gene was positive-weak in 18 (41%), moderate in 19 (41%), and strong in 6 (13%; P = .000). When we correlated PTEN + PCNA, it was P =.004, and PTEN + PTTG-1, it was P = .019. And when we correlated PCNA + PTGG-1, it was P = .262. In our results, we observed higher expression of PCNA-LI and PTTG-1 and loss of expression of PTEN. Nonfunctional hypophysis adenomas presented a higher PCNA, PTTG-1, and PTEN expression than functional ones. There was no difference between single-hormone-producing hypophysis adenomas or multiple-hormone-producing ones. Necrosis and hemorrhage were associated with PTEN expression, whereas atypias and mitosis figures were associated to PTTG-1 expression.