Expression of Matrix Metalloproteinase-9, Pituitary Tumor Transforming Gene, High Mobility Group A 2, and Ki-67 in Adrenocorticotropic Hormone–Secreting Pituitary Tumors and Their Association with Tumor Recurrence

Highlights

• MMP-9, PTTG, and HMGA2 and their associations with tumor recurrence after transsphenoidal adenomectomy remain unclear.

• A retrospective study was performed on 55 patients with sporadic CD with long-term remission after transsphenoidal adenomectomy.

• The expression level of MMP-9 was significantly increased in the recurrent group compared with the nonrecurrent group (P = 0.022) and strongly related to the recurrence-free interval (P = 0.007, CC = –0.354).

• PTTG, HMGA2, and Ki-67 expression showed no significant differences between the recurrent group and the nonrecurrent group.

• MMP-9 could be a valuable tool for predicting recurrence of ACTH-secreting pituitary tumors.

Objective

Matrix metalloproteinase-9 (MMP-9), pituitary tumor transforming gene (PTTG), and high mobility group A 2 (HMGA2) play important roles in the tumorigenesis of adrenocorticotrophic hormone (ACTH)-secreting pituitary tumors, but their associations with tumor recurrence after transsphenoidal adenomectomy remain unclear. The aim of the study was to investigate the immunohistochemical expression profiles of MMP-9, PTTG, HMGA2, and Ki-67 in recurrent and nonrecurrent ACTH-secreting pituitary tumors and to identify their associations with tumor behavior and recurrence status.

Methods

A retrospective study was performed including 55 patients with sporadic Cushing's disease with long-term remission after transsphenoidal adenomectomy. Fifty-five ACTH-secreting pituitary tumor specimens and 2 normal pituitary glands were collected. After an intensive follow-up (33–59 months, mean 41.8 months), patients were divided into 2 groups based on their recurrence status: the nonrecurrent group (n = 28) and the recurrent group (n = 27). The expression of MMP-9, PTTG, HMGA2, and Ki-67 in each sample was examined and quantified by immunohistochemistry. The association between MMP-9, PTTG, HMGA2, and Ki-67 expression and clinicopathologic characteristics and tumor recurrence were evaluated.

Results

There was a significantly increased expression of MMP-9 in the recurrent group compared with the nonrecurrent group (P = 0.022), and this was strongly associated with the recurrence-free interval (P = 0.007, correlation coefficient. = –0.354). PTTG, HMGA2, and Ki-67 expression were not significantly different between the recurrent group and the nonrecurrent group. No expression of MMP-9, PTTG, HMGA2, or Ki-67 was detected in the 2normal pituitary glands.

Conclusions

ACTH-secreting pituitary tumors with greater levels of MMP-9 were associated with a greater recurrence rate and a shorter recurrence-free interval. MMP-9 could be a valuable tool for predicting recurrence of ACTH-secreting pituitary tumors.

Introduction

Cushing disease (CD), caused by a pituitary corticotroph adenoma, comprises 70% of endogenous Cushing syndrome.¹ In Cushing's original series, the mean duration from presentation to death was 4.7 years.² In a recent multicenter, multinational, retrospective cohort study, compared with the general population, patients with CD who had been in remission for more than 10 years were at an increased risk of overall mortality, particularly from circulatory disease.³ Over the past 6 decades, even with advances in surgical techniques and medical treatment, CD remains associated with significant morbidity, especially metabolic and cardiovascular complications, osteoporosis, psychiatric changes, and cognitive impairment, as a result of chronic hypercortisolism.

Although transsphenoidal adenomectomy is the first treatment of choice, with immediate postoperative remission rates ranging between 65% and 90%, tumor recurrence rates are as high as 12%–45%, leading to a therapeutic challenge for endocrinologists and neurosurgeons.4, 5 The second line of therapy includes radiotherapy, bilateral adrenalectomy, and medical treatment.⁵ Specific medical therapies are categorized based on their mechanism of action: pituitary-directed (cabergoline and pasireotide), adrenal/steroidogenesis-directed (ketoconazole, metyrapone, and mitotane), and end-tissue–directed/cortisol receptors (mifepristone).⁶ Pasireotide, which was granted approval by the Food and Drug Administration for the treatment of CD in December 2012, is of particular utility in patients who are not eligible for surgery or patients with recurrence.⁷

Although some clinical predictive factors, such as postoperative serum cortisol levels and corticotropin-releasing hormone tests, have been studied systematically and may be associated with tumor recurrence status,⁸ few studies have investigated the association between biomarkers and the risk of recurrence of adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. Therefore, it is important to identify effective biomarkers for predicting the proliferative potential and potential for recurrence of CD, with the aim of identifying CD recurrence early and initiating an appropriate follow-up and therapeutic protocol, thus avoiding long-term mortality.

Although the molecular mechanisms underlying the tumorigenesis and progression of ACTH-secreting pituitary tumors are still elusive, pituitary corticotroph adenomas are monoclonal.⁹ Recent studies have shown that USP8 is frequently mutated in CD and contributes to ACTH overproduction by enhancing the promoter activity of the proopiomelanocortin gene.10, 11 However, no biomarkers have been reliably associated with tumor behavior and the recurrence of CD.

A large number of studies have suggested that matrix metalloproteinase-9 (MMP-9), pituitary tumor transforming gene (PTTG), and high mobility group A 2 (HMGA2) play key roles in the development of pituitary adenomas. Human PTTG was initially isolated from pituitary tumor cells and identified as securin, which is a protein regulating chromosome separation. PTTG is abundantly expressed in pituitary tumors and is a biological marker of malignancy grades in several forms of tumors, particularly endocrine tumors such as pituitary adenomas.¹² However, other studies have suggested that the expression of PTTG was not significantly associated with tumor invasiveness in patients with pituitary adenomas.¹³ Tumor-secreted matrix metalloproteinases degrade extracellular matrix, thus enabling tumor invasion. A previous study reported that MMP-9 may influence the invasiveness and recurrence of pituitary adenomas.¹⁴ HMGA2 is overexpressed in various benign and malignant tumors, is associated with a highly malignant phenotype, and is regarded as a poor prognostic indicator.¹⁵ Transgenic mice with overexpression HMGA2 develop pituitary adenomas that secrete prolactin and growth hormone, thus suggesting that HMGA2 may be involved in pituitary tumorigenesis.¹⁶

Whether MMP-9, PTTG, and HMGA2 are related to ACTH-secreting tumor recurrence is still unclear. In this study, we investigated the expression profile of MMP-9, PTTG, HMGA2, and Ki-67 in ACTH-secreting pituitary tumors and evaluated their association with tumor behavior and recurrence. Using this approach, we hope to identify molecular biomarkers to predict CD recurrence.