PDF icon Download PDF
Open Access
CC BY 4.0 · Indian Journal of Neurosurgery
DOI: 10.1055/s-0045-1811229
Original Article

PDZ Binding Kinase (PBK) Immunoexpression in Invasive Pituitary Adenomas: An Exploratory Study

Shilpa Rao
1   Department of Neuropathology, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka, India
,
Subhas Konar
2   Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka, India
,
A. Arivazhagan
2   Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka, India
,
Vani Santosh
1   Department of Neuropathology, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka, India
› Author Affiliations
› Further Information
Also available ateRefMedOne
 
 PDF Download Permissions and Reprints

Abstract

Background

Although pituitary adenomas (PAs) are believed to be benign neoplasms, invasion and recurrence are known in these tumors. Invasive PAs may not be amenable to complete excision and hence pose a challenge in the surgical management. Few previous studies have identified matrix metalloproteinase and vascular endothelial growth factor as possible contributors to invasion in PA, with no conclusive evidence. We studied the expression of a novel biomarker, PDZ-binding kinase (PBK) in invasive PA. PBK has earlier been shown to contribute to aggressiveness in glioblastoma, by our group.

Materials and Methods

A total of 23 invasive pituitary PAs were included. As controls, normal adenohypophysis and 10 noninvasive PAs were also studied. In all the cases, clinical, radiological, histopathological, and immunohistochemical profiles were analyzed. Invasion was defined based on radiological findings. Further, immunohistochemistry with PBK antibody was carried out and analyzed.

Results

Mean age in invasive PA was 47.6 years, in noninvasive PA was 48.6 years. The most common site of invasion was the cavernous sinus-unilateral (21.7%), and bilateral in 65.2%. The common presentation was vision involvement in both. The mean volume in the invasive group was 31.95 cc, and in the noninvasive group, it was 9.79 cc. The common surgical approach was the endoscopic transnasal approach in both groups. The majority of invasive (47.8%) and noninvasive (70%) PAs were gonadotroph adenomas. PBK immunopositivity was noted in 20/23 (87%) invasive PAs, while it was not observed in normal adenohypophysis or in any of the 10 noninvasive PAs.

Conclusion

PBK is a highly sensitive immunohistochemical marker for invasive PA, which can be used for identifying and predicting invasion. The upfront adjuvant therapy can be planned based on the invasiveness of the PA.


 

Keywords

PBK - invasive - pituitary adenoma - immunohistochemistry - recurrence

Introduction

Pituitary adenomas (PAs) are a group of neuroendocrine tumors known to arise from the adenohypophyseal cells.[1] Although most PAs are benign, invasion and recurrences are known and hence the recommendation to use the new terminology of PitNET (pituitary neuroendocrine tumor).[1] Invasive PAs are not amenable to complete surgical resection and thus pose a challenge to management. Invasive PA is defined as Knosp grade 3 and 4 with parasellar and cavernous sinus involvement.[2] The gross total resection rate also was poor in Knosp grade 3 or 4 tumors. Understanding the pathobiology of invasive PA is essential to guide comprehensive treatment. Few previous studies have identified angiogenesis and epithelial–mesenchymal transition factors as possible contributors to invasion in PA, although with no conclusive evidence.[3] PDZ-binding kinase (PBK) is a protein related to the mitogen-activated protein kinase kinase (MAPKK) family.[4] PDZ is an acronym of three proteins—postsynaptic density protein (PSD95), Drosophila disc large tumor suppressor (DlgA), and zonula occludens-1 protein (zo-1)—which were the first discovered to share the domain. It is known to play important roles in tumorigenesis of breast, lung, and prostate cancers.[5] [6] [7] Recently, our group has shown the role of PBK in the pathogenesis of invasion of glioblastoma (GBM). In this study, we aimed to analyze the immunoexpression of PBK in invasive PA compared to noninvasive PA.


 

Materials and Methods

This retrospective study included the invasive PA operated at our institute during the years 2018 to 2023 (5 years). Normal adenohypophysis and noninvasive PA were considered as controls. Adenohypophysial control tissue was obtained from postmortem samples usually 4 to 6 hours after death. The clinical, radiological, histopathological, and immunohistochemical (hormone) profiles were analyzed in all cases. Invasion was defined based on radiological findings. Hematoxylin and eosin (H&E)-stained sections were examined followed by immunohistochemical panel that included cytokeratin (ThermoFisher, 1:200), growth hormone (Biogenex, GH/1450, 1:400), prolactin (Biogenex, PRL/2644, 1:100), thyroid-stimulating hormone (Biogenex, 5404, 1:100), luteinizing hormone (Biogenex, SP132, 1:500), follicle-stimulating hormone (BioSB, EP257, 1:100), adrenocortical hormone (Biogenex, A26, 1:100), Pit1 (Abcam, 2c11, 1:200), SF1 (Abcam, EPR19744, 1:1,000), TPIT (Abcam, CL62511, 1:1,000), and Ki-67 (DAKO, MIB1, 1:200). Further, immunohistochemistry (IHC) with PBK antibody (Abcam, EP2520Y, 1:50) was carried out and analyzed. IHC was performed using automated Ventana benchmark. The study was conducted after Institutional Ethics Committee approval.


 

Results

A total of 23 invasive PAs were included in the study. As controls, two normal adenohypophysis and 10 noninvasive PAs were also studied.

Mean age in invasive PA was 47.6 years (standard deviation [SD]:10.17), and 48.6 years (SD:14.76) in noninvasive PA. Male preponderance was noted in invasive PA (M:F: 15:8), while no preponderance was observed in noninvasive PA (M:F: 1:1). Mean duration of symptoms was 23 months in the invasive group and 9.2 months in the noninvasive group. Visual symptoms in the form of blurring of vision and hemianopia were the most encountered symptoms in both followed by headache. There was a single case of pituitary apoplexy in each group. Among the invasive PA, the most common site of invasion was to cavernous sinus—unilateral (21.7%) or bilateral (65.2%). Other sites of invasion were the sphenoid sinus and the lateral ventricle ([Fig. 1A]). The mean tumor volume was 31.95 cc in the invasive group and 9.79 cc in the noninvasive group. The common surgical approach was endoscopic transnasal in both invasive (61.3%) and noninvasive (90%) groups ([Table 1]).

Zoom
Fig. 1 MRI brain (T2W, coronal) showing a sellar and suprasellar lesion with bilateral cavernous sinus invasion (L > R) (A; Knosp grade 4). Tumor shows acidophilic cells (B; H&E) with immunopositivity for growth hormone (C), cytokeratin (D) and diffuse, strong cytoplasmic positivity for PBK (E), and low proliferation (F; Ki67). H&E, hematoxylin and eosin; MRI, magnetic resonance imaging; T2W, T2-weighted.
Table 1

Demographics and clinical details

Invasive adenoma

Noninvasive adenoma

Number of patients

23

10

Age (mean, SD), y

47.65 (10.17)

48.6 (14.76)

Gender: male:female

15:8

5:5

Duration of symptoms, mean

23 mo

9.2 mo

Vision involved

21 (67.7%)

9 (90%)

Headache

10 (32.3%)

6 (60%)

Apoplexy

1 (3.2%)

1 (10%)

Volume, mean (SD)

31.95 (26.37)

9.79 (8.94)

Bilateral cavernous sinus

15 (65.2%)

NA

Unilateral cavernous sinus

5 (21.7%)

NA

Sphenoid sinus

2 (8.6%)

NA

Lateral ventricle

1 (4.3%)

NA

Surgery: TNTS:

19 (61.3%)

9 (90%)

 TC:

4 (12.9%)

1 (10%)

HPE:

 Gonadotroph adenoma

11 (47.8%)

7 (70%)

 Corticotroph adenoma

2 (8.6%)

3 (30%)

 Lactotroph adenoma

2 (8.6%)

Nil

 Null cell adenoma

1 (4.3%)

Nil

 Somatotroph adenoma

2 (8.6%)

Nil

 Mixed somatotroph–lactotroph adenoma

5 (21.7%)

Nil

Abbreviation: HPE, Histopathological examination; SD, standard deviation; TC, transcranial; TNTS, transnasal transsphenoidal surgery.


On pathological examination, among invasive PAs, 11 were gonadotroph adenomas, 5 mixed somatotroph–lactotroph adenomas, 2 somatotroph adenomas ([Fig. 1B–D]), 2 corticotroph adenomas, and 2 lactotroph adenomas. One invasive adenoma was null cell adenoma. Noninvasive PAs were predominantly gonadotroph adenoma (7/10). PBK expression was noted in the nucleus and cytoplasm of tumor cells like that in GBM. PBK immunopositivity was noted in 20/23 (87%) invasive PA, while it was not observed in normal adenohypophysis or in any of the 10 noninvasive PAs ([Fig. 2]). PBK immunoexpression varied from patchy to diffuse reactivity in tumor cells ([Table 2]).

Zoom
Fig. 2 MRI brain (T2W, coronal) showing hyperintense lesion in sellar and suprasellar region without invasion (A; Knosp grade 1). The tumor cells are in organoid nests (B; H&E) with diffuse immunopositivity for cytokeratin (C), negative for PBK (D) and hormones (E) with low proliferation (F; Ki67). Magnification = scale bar. H&E, hematoxylin and eosin; MRI, magnetic resonance imaging; T2W, T2-weighted.
Table 2

PBK immunoexpression in invasive pituitary adenomas

Invasive pituitary adenoma

PBK immunoexpression

Mixed somatotroph–lactotroph adenoma (n = 5)

Positive (5/5)

Gonadotroph adenoma (n = 11)

Positive (11/11)

Somatotroph adenoma (n = 2)

Positive (2/2)

Lactotroph adenoma (n = 2)

Positive (1/2)

Corticotroph adenoma (n = 2)

Positive (1/2)

Null cell adenoma (n = 1)

Negative (1/1)

Abbreviation: PBK, PDZ-binding kinase.



 

Discussion

PAs account for 10 to 25% of all intracranial tumors. Although most PAs have benign morphology, about 35% of PAs are invasive.[3] The need to identify this group of PAs is essential as they are not amenable to complete excision leading to high morbidity. Hence, adjuvant therapy needs to be administered to reduce the incidence of recurrence or further growth. Understanding the underlying genetic alterations would be necessary to elucidate the mechanisms of invasiveness in PA, which can be further targeted using agents specific to these alterations or pathways. Although the third edition of classification of endocrine tumors introduced the entity of atypical PA, which was characterized by p53 positivity and Ki67 labelling of >3%, the fourth edition of classification did not recognize atypical PA as an aggressive type and hence this entity was removed.[8] [9] In the World Health Organization CNS5, terminology of PitNET is recommended to indicate the invasive and metastatic potential of PA.[10] Sparsely granulated PA, silent corticotroph adenoma, crooke cell adenoma, Pit-1-positive plurihormonal adenoma, and lactotroph adenoma in men are the histological types of PA which are known to behave aggressively. Histological subtype of PA does not determine invasiveness in PA.[11]

Studies by research groups have looked at the possible role of hypoxia-inducible factor-1a, pituitary tumor-transforming gene (PTTG), vascular endothelial growth factor (VEGF), fibroblast growth factor-2, and matrix metalloproteinases (MMPs, mainly MMP-2, and MMP-9) in the pathobiology of PA.[12] As these molecules are involved in cell proliferation, epithelial-to-mesenchymal transition, angiogenesis, degradation, and remodeling of extracellular matrix, they are believed to be the core molecules responsible for the invasiveness in PA.[3] Hypoxia, either induced by necrosis or apoplexy, results in the release of hypoxia-inducible factor-1a, which acts as the initiating factor for invasiveness, and in turn causes overexpression of VEGF responsible for angiogenesis.[13] [14] VEGF further activates multiple downstream pathways, which result in endothelial proliferation, endothelial migration, and increase vascular permeability.[15] MMP and PTTG alter the stromal microenvironment aiding in invasion.[16] [17] [18] However, no single biomarker has been found to independently predict aggressive behavior in pituitary neoplasms.

We studied immunoexpression of PBK in invasive PA and compared with noninvasive PA as well as the expression in nonneoplastic adenohypophyseal cells. Our previous study had identified a significant role of PBK in the invasiveness of GBM.[19] PBK mRNA and protein expression were significantly upregulated in peritumoral brain zone compared to the tumor core. PBK was also overexpressed in recurrent GBM. PBK has also been implicated in other systemic malignancies including prostate cancer where it is believed to function through activation of MMPs. The therapeutic role of a PBK inhibitor has been observed in glioma-initiating cell cultures.[20] In our in vitro study on GBM, PBK knockdown in GBM cell lines resulted in increased sensitivity to chemotherapeutic drugs and radiation exposure, indicating a role of PBK in radio-chemoresistance.[19] These results encouraged us to study immunoexpression of PBK in invasive PA.

We observed that the majority of invasive PAs expressed PBK on IHC, whilst none of the noninvasive PA or the normal adenohypophyseal cells were immunopositive for PBK, suggesting that PBK is one of the biomarkers associated with invasiveness in PA. PBK is known to contribute to invasion and metastasis in breast, lung, and prostate malignancies through activation of MMP-2 and MMP-9, with beta-catenin acting as an intermediary.[21] MMPs aid in invasion through degradation of the matrix in the tumor microenvironment. Small-molecule inhibitors targeting PBK have great therapeutic potential in the treatment of cancer. Targeting PBK could be more beneficial in addressing invasiveness.[7] [22]


 

Conclusion

Our study identifies a novel biomarker PBK. PBK is a highly sensitive immunohistochemical marker for invasive PA. Functional studies are required to establish its role in invasiveness of PA, which could probably lead to development of targeted therapy in invasive PA.


 

 

Conflict of Interest

None declared.


Address for correspondence

Shilpa Rao, DM
Department of Neuropathology, NIMHANS
Bangalore, Karnataka 560029
India   

Publication History

Article published online:
13 August 2025

© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)

Thieme Medical and Scientific Publishers Pvt. Ltd.
A-12, 2nd Floor, Sector 2, Noida-201301 UP, India


  Permissions and Reprints
Zoom
Fig. 1 MRI brain (T2W, coronal) showing a sellar and suprasellar lesion with bilateral cavernous sinus invasion (L > R) (A; Knosp grade 4). Tumor shows acidophilic cells (B; H&E) with immunopositivity for growth hormone (C), cytokeratin (D) and diffuse, strong cytoplasmic positivity for PBK (E), and low proliferation (F; Ki67). H&E, hematoxylin and eosin; MRI, magnetic resonance imaging; T2W, T2-weighted.
Zoom
Fig. 2 MRI brain (T2W, coronal) showing hyperintense lesion in sellar and suprasellar region without invasion (A; Knosp grade 1). The tumor cells are in organoid nests (B; H&E) with diffuse immunopositivity for cytokeratin (C), negative for PBK (D) and hormones (E) with low proliferation (F; Ki67). Magnification = scale bar. H&E, hematoxylin and eosin; MRI, magnetic resonance imaging; T2W, T2-weighted.