Clinical and cytofunctional classification of pituitary adenomas: proposal of a new classification

Outcomes of surgically treated giant pituitary tumours

OBJECTIVE

To evaluate the outcomes of patients with giant pituitary tumours (GPTs) who underwent a purely binasal endoscopic transsphenoidal surgery (BETS) and compare their outcomes with those achieved through craniotomy and microscopic transsphenoidal surgery (MTS).

METHODS

Seventy-two consecutive patients with GPTs (greater than 10 cm3 in volume) who were treated surgically with BETS, craniotomy, or MTS from October 1994 to July 2009 were reviewed for clinical outcomes, degree of tumor resection, recurrence rates, and surgical complications.

RESULTS

The BETS group had significantly better mean reduction of tumor volume (91%) than the craniotomy (63%, p = 0.001), and the MTS (63%, p = 0.010) groups. Gross total resection rates were also higher for BETS patients than for craniotomy patients (p = 0.010). Improvements in vision and headaches were noted in 96% and 100% of patients in the BETS group, respectively; these rates were similar to those in the craniotomy and MTS groups. Of the four patients with hormone-secreting tumours in the BETS group, three remained in remission. The median length-of-stay (four days) for the BETS group was shorter (p = 0.010), and surgical complications were less frequent (p = 0.037) and less severe compared to the craniotomy group. There were no differences in the recurrence rates: 79% percent of patients in the BETS group, 69% in the craniotomy group, and 79% in the MTS group were recurrence free at last follow-up (p = 0.829).

CONCLUSIONS

Treatment of GPT with BETS offers excellent oncologic and clinical outcomes and can frequently obviate the need for craniotomy in these patients.

Expression of MSX1 in human normal pituitaries and pituitary adenomas

Transcription factors play specific roles in the development and differentiation of normal pituitary tissues and pituitary adenoma. The transcription factor, muscle segment homeobox 1 (MSX1), which belongs to the homeobox gene family, binds the promoter region of the glycoprotein hormone alpha-subunit (SU) in TSH-producing cells in the mouse pituitary and regulates alpha-SU expression. The present study investigated MSX1 expression in the normal human pituitary. In addition, 50 pituitary adenomas were examined using immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR) to clarify the role of MSX1 in the development and functional differentiation of pituitary adenoma cells. In the normal pituitary, MSX1 was predominantly expressed in the cytoplasm of GH-producing cells. Furthermore, MSX1 immunoreactivity was observed in the cytoplasm of some alpha-SU-producing cells. It is interesting to note that, in the pituitary adenoma, MSX1 was expressed in the nucleus of GH- and TSH-producing adenomas. RT-PCR using RNA extracted and purified from formalin-fixed paraffin-embedded pituitary adenoma specimens revealed MSX1 mRNA expressed in GH- and TSH-producing adenomas. Immunoelectron microscopy demonstrated MSX1 localized at intranuclear heterochromatin and euchromatin, which suggests transcriptional activity. These results suggest that MSX1 plays a specific role in human pituitary adenoma.

Cytochemical and molecular biological aspects of the pituitary and pituitary adenomas--cell differentiation and transcription factors

The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.

Expression of GATA-2 in human pituitary adenomas

Transcription factor GATA-2 contains two copies of a highly conserved zinc finger domain and plays unique roles at an early stage of hematopoietic differentiation. In the mouse pituitary gland, Pit-1-GATA-2 protein-protein interaction has been shown to lead to gene-specific actions to obtain cell-specific roles. In this study, we investigated the expression of GATA-2 and Pit-1 in human pituitary adenomas using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical techniques. By immunohistochemical analysis, GATA-2 was detected in all of the gonadotropin-subunit (Gn-su)-positive adenomas (n = 8) and in four of five thyroid-stimulating hormone (TSH)-secreting adenomas, but its incidence was low in the other types of adenomas. Pit-1 protein was detected in 4 of 5 TSH-secreting adenomas and in 10 of 10 growth hormone (GH)-secreting adenomas. By RT-PCR analysis, GATA-2 was detected in all Gn-su-positive adenomas and TSH-secreting adenomas, and Pit-1 was detected in all TSH-secreting adenomas and GH-secreting adenomas. These results suggested that GATA-2 contributes to the functional expression and the differentiation of Gn-su-positive adenomas and the TSH-secreting adenomas and that the interaction between GATA-2 and Pit-1 can lead to gene-specific action and differentiation of TSH-secreting adenomas. It is further speculated that GATA-2 and transcriptional interaction with Pit-1 play roles in the functional differentiation of specific pituitary adenomas.

Immunohistochemical analysis of RCAS1 in human pituitary adenomas

It has been reported that RCAS1 (receptor-binding cancer antigen expressed on SiSO cells) acts as a ligand for a receptor present on normal peripheral lymphocytes and induces apoptotic cell death. It is expressed in uterine and ovarian carcinomas, especially in invasive cancers. This immunohistochemical study is aimed to elucidate the expression of RCAS1 in human pituitary adenomas in order to clarify its role in their proliferative regulation and invasiveness. Five normal pituitary glands, 50 human pituitary adenomas, and one malignant glioma were subjected to immunohistochemical studies. In normal pituitary glands, immunostaining of RCAS1 and MIB-1 was not found. In malignant glioma, large numbers of cell nuclei were positive for MIB-1 (MIB-1 index: 28%), and RCAS1 was detected both in the cytoplasm and on the membrane of the tumor cells. Expression of RCAS1 was noted in 48% of pituitary adenomas immunohistochemically (60.0% of growth hormone-secreting adenomas, 60.0% of prolactin-secreting adenomas, 42.9% of adrenocorticotrophin-secreting adenomas, 40.0% of thyroid-stimulating hormone-secreting adenomas, 33.3% of nonfunctioning adenomas, and 44.4% of gonadotropin-subunit-positive adenomas). It showed no correlation with tumor type, size, and invasiveness. The statistically significant relationship between RCAS1 and MIB-1 positivity was identified in our study. These results suggest that expression of RCAS1 as well as MIB-1 positivity predict the growth potential of individual pituitary adenomas.

Expression of neuro D1 in human normal pituitaries and pituitary adenomas

Neuro D1 is a basic helix-loop-helix transcription factor expressed in the endocrine cells of pancreas and in a subset of neurons as they undergo terminal differentiation. In the adult pituitary gland, Neuro D1 is expressed in corticotroph cells and contributes to the corticotroph-specific pro-opiomelanocortin (POMC) transcription by interacting with Pituitary homeobox 1 (Ptx 1) transcription factor. In the present study, we investigated the expression of Neuro D1 in human normal pituitaries and different types of human pituitary adenomas using the RT-PCR and immunohistochemical techniques. Using RT-PCR, Neuro D1 mRNA was found to be expressed in ACTH-secreting adenomas (n = 3) and 6 of 8 non-functioning adenomas. On the other hand, GH-secreting adenomas (n = 5) and PRL-secreting adenomas (n = 3) were completely negative for Neuro D1 mRNA. Immunohistochemically, Neuro D1 was expressed in all ACTH-secreting adenomas (n = 10), and in 14 of 20 nonfunctioning adenomas. In contrast, 3 of 10 PRL-secreting adenomas and 2 of 10 GH-secreting adenomas showed positive Neuro D1 staining in the nuclei. The above results suggest that Neuro D1 contribute to the functional expression and the differentiation of ACTH-secreting adenomas. It also appears from our study that Neuro D1 might play a role in the differentiation of non-functioning adenomas, the mechanism of which remains to be further investigated. This is the first study on Neuro D1 in case of human pituitary adenomas.

Expression of pituitary homeo box 1 (Ptx1) in human non-neoplastic pituitaries and pituitary adenomas

We investigated the localization of pituitary homeo box 1 (Ptx1) protein in five human non-neoplastic pituitaries and 73 of all types of pituitary adenomas using immunohistochemistry, and the expression of Ptx1 messenger RNA (mRNA) in 18 representative pituitary adenomas using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. By immunohistochemical analysis, Ptx1 protein was extensively detected in the nuclei of normal human pituitary cells. Ptx1 was detected in 10/14 (71.4%) of growth hormone (GH)-secreting adenomas, 12/12 (100%) of prolactin (PRL)-secreting adenomas, 18/20 (90%) of adrenocorticotropic hormone (ACTH)-secreting adenomas, 6/7 (85.7%) of thyroid-stimulating hormone (TSH)-secreting adenomas, and 17/20 (85%) of clinically non-functioning adenomas, including 9/10 (90%) of gonadotropin-subunit-positive adenomas. Thus, there was no relationship between Ptx1 expression and a particular type of pituitary adenomas. By RT-PCR analysis, Ptx1 mRNA was expressed in all 18 cases of pituitary adenomas, including two cases negative for Ptx1 protein by immunohistochemistry. These results suggested that Ptx1 may be an universal transcription factor in both neoplastic and non-neoplastic conditions in human pituitaries. The synergistic action with other transcription factors may be speculated to determine the specific production of the anterior pituitary hormones.

Molecular Pathology of the Pituitary Adenomas

Molecular techniques have been applied to the study of pituitary adenomas by many investigators. We have used nonisotopic in situ hybridization (ISH) to analyze pituitary adenomas in our laboratory. These studies have provided insight into mRNA production by various adenomas, and have contributed toward our new proposed clinical and cytofunctional classification of pituitary adenomas.