Temozolomide therapy in a man with an aggressive prolactin-secreting pituitary neoplasm: Morphological findings

[Prolactin-secreting pituitary carcinomas with intra- and extracranial metastasis: case report and review]

According to the modern WHO classification, pituitary carcinomas (or metastatic neuroendocrine pituitary tumors) are pituitary tumors with confirmed craniospinal and/or distant metastases. The main goal of histological analysis of pituitary carcinomas is to confirm pituitary origin of metastases. Treatment usually includes surgery and radiotherapy, dopamine agonists in maximum possible doses in case of prolactin-secreting pituitary carcinomas and chemotherapy with preferable temozolomide.

OBJECTIVE

To present the results of diagnosis and treatment of two patients with prolactin-secreting pituitary carcinomas.

MATERIAL AND METHODS

The authors describe 2 patients with prolactin-secreting pituitary carcinomas arising from drug-resistant aggressive prolactinomas with histologically confirmed metastases. In both cases, combined treatment included surgery, radio- and chemotherapy (cabergoline and temozolomide).

RESULTS

A 47-year-old patient underwent surgery, radio- and dopamine agonist therapy with subsequent regression of tumor growth in the follow-up period. However, progressive increase in prolactin concentration necessitated PET/CT with detection of multiple metastases in bones and lymph nodes. Temozolomide therapy led to temporary shrinkage of metastatic foci with subsequent progression. The second case was characterized by multiple brain and spinal cord metastases in a 47-year-old woman. Resection of intracranial metastasis and temozolomide therapy stabilized the disease and normalized serum prolactin throughout 2-year follow-up with subsequent progression.

CONCLUSION

Pituitary carcinoma is a rare tumor with unfavorable prognosis. Treatment is currently not standardized and determined by available world experience regarding various chemotherapeutic drugs. Temozolomide is the most effective drug. However, short-term remission is usually followed by subsequent disease progression in most cases.

MGMT in TMZ-based glioma therapy: Multifaceted insights and clinical trial perspectives

Temozolomide (TMZ) is the most preferred and approved chemotherapeutic drug for either first- or second-line chemotherapy for glioma patients across the globe. In glioma patients, resistance to treatment with alkylating drugs like TMZ is known to be conferred by exalted levels of MGMT gene expression. On the contrary, epigenetic silencing through MGMT gene promoter methylation leading to subsequent reduction in MGMT transcription and protein expression, is predicted to have a response favoring TMZ treatment. Thus, MGMT protein level in cancer cells is a crucial determining factor in indicating and predicting the choice of alkylating agents in chemotherapy or choosing glioma patients directly for a second line of treatment. Thus, in-depth research is necessary to achieve insights into MGMT gene regulation that has recently enticed a fascinating interest in epigenetic, transcriptional, post-transcriptional, and post-translational levels. Furthermore, MGMT promoter methylation, stability of MGMT protein, and related subsequent adaptive responses are also important contributors to strategic developments in glioma therapy. With applications to its identification as a prognostic biomarker, thus predicting response to advanced glioma therapy, this review aims to concentrate on the mechanistic role and regulation of MGMT gene expression at epigenetic, transcriptional, post-transcriptional, and post-translational levels functioning under the control of multiple signaling dynamics.

Metastatic pituitary tumors: an institutional case series

PURPOSE

Pituitary carcinomas are a rare entity that respond poorly to multimodal therapy. Patients follow a variable disease course that remains ill-defined.

METHODS

We present an institutional case series of patients treated for pituitary carcinomas over a 30-year period from 1992 to 2022. A systematic review was conducted to identify prior case series of patients with pituitary carcinomas.

RESULTS

Fourteen patients with a mean age at pituitary carcinoma diagnosis of 52.5 years (standard deviation [SD] 19.4) met inclusion criteria. All 14 patients had tumor subtypes confirmed by immunohistochemistry and hormone testing, with the most common being ACTH-producing pituitary adenomas (n = 12). Patients had a median progression-free survival (PFS) of 1.4 years (range 0.7-10.0) and a median overall survival (OS) of 8.4 years (range 2.3-24.0) from pituitary adenoma diagnosis. Median PFS and OS were 0.6 years (range 0.0-2.2) and 1.5 years (range 0.1-9.6) respectively upon development of metastases. Most patients (n = 12) had locally invasive disease to the cavernous sinus, dorsum sellae dura, or sphenoid sinus prior to metastasis. Common sites of metastasis included the central nervous system, liver, lung, and bone. In a pooled analysis including additional cases from the literature, treatment of metastases with chemotherapy or a combination of radiation therapy and chemotherapy significantly prolonged PFS (p = 0.02), while failing to significantly improve OS (p = 0.14).

CONCLUSION

Pituitary carcinomas are highly recurrent, heterogenous tumors with variable responses to treatment. Multidisciplinary management with an experienced neuro-endocrine and neuro-oncology team is needed given the unrelenting nature of this disease.

β-Catenin is reduced in membranes of human prolactinoma cells and it is inhibited by temozolomide in prolactin secreting tumor models

INTRODUCTION: Prolactinomas are the most frequent pituitary tumor subtype. Despite most of them respond to medical treatment, a proportion are resistant and become a challenge in clinical management. Wnt/β-Catenin pathway has been implicated in several cancers including pituitary tumors and other sellar region malignancies. Interestingly, Wnt/β-Catenin inhibition augments the cytotoxicity of the chemotherapeutic agent Temozolomide (TMZ) in different cancers. TMZ is now being implemented as rescue therapy for aggressive pituitary adenoma treatment. However, the molecular mechanisms associated with TMZ action in pituitary tumors remain unclear. OBJECTIVES: Our aims in the present study were to evaluate differential β-Catenin expression in human resistant prolactinomas and Wnt/β-Catenin signaling activation and involvement in Prolactin (PRL) secreting experimental models treated with TMZ. RESULTS: We first evaluated by immunohistochemistry β-Catenin localization in human resistant prolactinomas in which we demonstrated reduced membrane β-Catenin in prolactinoma cells compared to normal pituitaries, independently of the Ki-67 proliferation indexes. In turn, in vivo 15 mg/kg of orally administered TMZ markedly reduced PRL production and increased prolactinoma cell apoptosis in mice bearing xenografted prolactinomas. Intratumoral β-Catenin strongly correlated with Prl and Cyclin D1, and importantly, TMZ downregulated both β-Catenin and Cyclin D1, supporting their significance in prolactinoma growth and as candidates of therapeutic targets. When tested in vitro, TMZ directly reduced MMQ cell viability, increased apoptosis and produced G2/M cell cycle arrest. Remarkably, β-Catenin activation and VEGF secretion were inhibited by TMZ in vitro. CONCLUSIONS: We concluded that dopamine resistant prolactinomas undergo a β-Catenin relocalization in relation to normal pituitaries and that TMZ restrains experimental prolactinoma tumorigenicity by reducing PRL production and β-Catenin activation. Together, our findings contribute to the understanding of Wnt/β-Catenin implication in prolactinoma maintenance and TMZ therapy, opening the opportunity of new treatment strategies for aggressive and resistant pituitary tumors.

Aggressive prolactinomas responsive to temozolomide treatment: Report of two cases

Refractory aggressive prolactinomas are detected after the unresponsiveness to conventional therapies. We report two cases that underwent temozolomide treatment and have been in near-complete remission ever since. We suggest the pathology techniques for earlier detection and, subsequently, treatment with temozolomide to reduce morbidities and better respond to therapy.

High-risk pituitary adenomas and strategies for predicting response to treatment

High-risk pituitary adenomas are aggressive. They show clinical and imaging features similar to those of carcinomas, including infiltration of the surrounding brain structures, but lack cerebrospinal or systemic metastases. In addition, they display distinct behavior, including tendency for fast growth and frequent recurrences, which are difficult to control. The term "high-risk" adenoma was first introduced in the 4th edition of the World Health Organization Classification of Endocrine Tumors in 2017. Five defined adenoma types belong to this category, including sparsely granulated somatotroph, lactotroph in men, Crooke cell, silent corticotroph, and plurihormonal PIT-1 positive adenomas. The morphological and immunohistochemical characteristics of high-risk adenomas are herein described in detail. In addition, the clinical features and the treatment options are presented. This review focuses on predictive markers assessed by immunohistochemistry, which help clinicians to design the appropriate treatment strategies for high-risk adenomas. Somatostatin receptor status predicts effectiveness of postsurgical treatment with somatostatin analogs, and MGMT expression predicts response to treatment with temozolomide. This comprehensive review presents the clinical and pathological features of high-risk pituitary adenomas, underlines the contribution of immunohistochemistry, and emphasizes the leading role of pathology in the design of optimal clinical management.

MGMT immunohistochemistry in pituitary tumors: controversies with clinical implications

INTRODUCTION

Temozolomide (TMZ) is currently considered as a rational therapeutic option for patients with progressively aggressive pituitary adenomas and carcinomas not responding to conventional therapies. Administration of TMZ results in clinical response and improvement in survival of many of these patients depending upon the expression of the DNA repair enzyme O-6 methylguanine DNA transferase (MGMT). Low or negative MGMT immunoreactivity predicts responsiveness to TMZ therapy. Therefore, MGMT serves as a criterion to select candidate patients anticipating response to treatment.

MATERIALS AND METHODS

The MGMT expression was investigated in 25 pituitary adenomas with Ki-67 labeling index more that 3% and p53 expression, using various antigen retrieval protocols. After direct application of the antibody, only one adenoma yielded positive for MGMT. However, after pretreatment of tissue sections with antigen retrieval protocols, another 3 adenomas, initially negative turned to positive.

CONCLUSIONS

These findings could explain lack of response to TMZ treatment in patients with false negative MGMT immunohistochemistry. Evaluation of tumor samples for MGMT expression should carefully be carried-out using the optimum immunohistochemical protocol to obtain consistent and reliable results that help to identify patients that could respond to TMZ therapy.

Aggressive and malignant pituitary tumours: state-of-the-art

Pituitary adenomas are unique in multiple ways. They are rarely malignant in terms of metastases; yet, they may be aggressive. Their cancerous potential is defined in a classic oncological way by the ability to metastasise, and therefore, it has been crucial to differentiate this process from aggressive behaviour, characterised as a particularly invasive and/or recurrent behaviour and resistance to common modalities of therapy. Recently, however, important changes have been introduced to the diagnosis and management of aggressive and malignant pituitary tumours including the 4th edition of the World Health Organization (WHO) classification for endocrine tumours (2017) as well as ESE Clinical Guidelines (2018), although an attempt to establish predictive and/or prognostic markers of clinical aggressiveness remains difficult. In this review, we focus on a group of pituitary tumours causing significant problems in clinical practice and requiring multidisciplinary input. We summarise updates in definitions of tumour invasiveness, aggressiveness and malignant transformation, as well as histological classification, and emphasise the new considerations regarding aggressive and malignant potential and its relationship to therapeutic strategies.

65 YEARS OF THE DOUBLE HELIX: Treatment of pituitary tumors with temozolomide: an update

Temozolomide is an alkylating chemotherapeutic agent used in malignant neuroendocrine neoplasia, melanoma, brain metastases and an essential component of adjuvant therapy in the treatment of glioblastoma multiforme and anaplastic astrocytoma. Since 2006, it has been used for the treatment of pituitary carcinomas and aggressive pituitary adenomas. Here, we discuss the current indications and results of temozolomide therapy in pituitary tumors, as well as frequently asked questions regarding temozolomide treatment, duration of therapy, dosage, tumor recurrence and resistance.

Treatment of Aggressive Prolactin-Secreting Pituitary Adenomas with Adjuvant Temozolomide Chemotherapy: A Review

Most prolactin-secreting pituitary adenomas demonstrate slow growth and are effectively managed with medical/surgical therapy. Rarely, these tumors can behave aggressively with rapid growth and invasion of local tissues, and are refractory to medical, surgical, or radio-surgical therapies. We report a case of a prolactin-secreting adenoma in a young woman, which became progressively aggressive and refractory to usual treatment modalities, but responded to treatment with the chemotherapeutic agent temozolomide. In addition, we review the literature for treatment of refractory adenomas with temozolomide. The clinical and pathologic characteristics of aggressive prolactin-secreting adenomas are reviewed, as well as their response to dopamine agonists, surgery, radiotherapy, and chemotherapy.

Temozolomide treatment of pituitary carcinomas and atypical adenomas: systematic review of case reports

BACKGROUND

Pituitary carcinomas (PC) and atypical pituitary adenomas (APA) are rare variants of pituitary tumors for which no evidence-based treatment currently exists. We sought to determine whether temozolomide represents an effective chemotherapeutic option for patients with PC and APA.

METHODS

A systematic review was performed using all published cases of PC and APA treated with temozolomide, and for which information on treatment regimen, clinical response, and survival could be identified. The primary goal of this analysis was to describe overall survival and progression-free survival among PC and APA patients after temozolomide treatment. Secondary goals included assessment of response rate and biomarkers of response.

RESULTS

We identified 57 cases and obtained follow-up data on 54 patients (31 APA and 23 PC) for analysis. Estimates of 5-year progression-free survival and overall survival were 21.9% and 57.4% for patients with APA and 36.1% and 56.2% for patients with PC. Among those who responded to temozolomide, overall survival was marginally statistically significantly greater for patients on long-term temozolomide therapy compared with those who were not (5-year overall survival 91.7% vs 54.1%, P = .08); Progression-free survival results were similar but not statistically significant. The objective response rate was 48.4% for patients with APA and 65.2% for patients with PC. Stable disease occurred in 29% of APA and 17.4% of PC patients. Neither histology nor expression of Ki-67 correlated with response; however, negative O⁶-methylguanine-DNA methyltransferase staining was strongly related to response to temozolomide in patients with APA (P < .001).

CONCLUSIONS

Temozolomide is an effective treatment of both PC and APA, and long-term treatment can be considered for particularly aggressive cases.

Nelson's syndrome: a review of the clinical manifestations, pathophysiology, and treatment strategies

Nelson's syndrome is a rare clinical manifestation that occurs in 8%-47% of patients as a complication of bilateral adrenalectomy, a procedure that is used to control hypercortisolism in patients with Cushing's disease. First described in 1958 by Dr. Don Nelson, the disease has since become associated with a clinical triad of hyperpigmentation, excessive adrenocorticotropin secretion, and a corticotroph adenoma. Even so, for the past several years the diagnostic criteria and management of Nelson's syndrome have been inadequately studied. The primary treatment for Nelson's syndrome is transsphenoidal surgery. Other stand-alone therapies, which in many cases have been used as adjuvant treatments with surgery, include radiotherapy, radiosurgery, and pharmacotherapy. Prophylactic radiotherapy at the time of bilateral adrenalectomy can prevent Nelson's syndrome (protective effect). The most promising pharmacological agents are temozolomide, octreotide, and pasireotide, but these agents are often administered after transsphenoidal surgery. In murine models, rosiglitazone has shown some efficacy, but these results have not yet been found in human studies. In this article, the authors review the clinical manifestations, pathophysiology, diagnostic criteria, and efficacy of multimodal treatment strategies for Nelson's syndrome.

The Treatment of Cushing's Disease

Cushing's disease (CD), or pituitary-dependent Cushing's syndrome, is a severe endocrine disease caused by a corticotroph pituitary tumor and associated with increased morbidity and mortality. The first-line treatment for CD is pituitary surgery, which is followed by disease remission in around 78% and relapse in around 13% of patients during the 10-year period after surgery, so that nearly one third of patients experience in the long-term a failure of surgery and require an additional second-line treatment. Patients with persistent or recurrent CD require additional treatments, including pituitary radiotherapy, adrenal surgery, and/or medical therapy. Pituitary radiotherapy is effective in controlling cortisol excess in a large percentage of patients, but it is associated with a considerable risk of hypopituitarism. Adrenal surgery is followed by a rapid and definitive control of cortisol excess in nearly all patients, but it induces adrenal insufficiency. Medical therapy has recently acquired a more important role compared to the past, due to the recent employment of novel compounds able to control cortisol secretion or action. Currently, medical therapy is used as a presurgical treatment, particularly for severe disease; or as postsurgical treatment, in cases of failure or incomplete surgical tumor resection; or as bridging therapy before, during, and after radiotherapy while waiting for disease control; or, in selected cases, as primary therapy, mainly when surgery is not an option. The adrenal-directed drug ketoconazole is the most commonly used drug, mainly because of its rapid action, whereas the glucocorticoid receptor antagonist, mifepristone, is highly effective in controlling clinical comorbidities, mainly glucose intolerance, thus being a useful treatment for CD when it is associated with diabetes mellitus. Pituitary-directed drugs have the advantage of acting at the site responsible for CD, the pituitary tumor. Among this group of drugs, the dopamine agonist cabergoline and the somatostatin analog pasireotide result in disease remission in a consistent subgroup of patients with CD. Recently, pasireotide has been approved for the treatment of CD when surgery has failed or when surgery is not an option, and mifepristone has been approved for the treatment of Cushing's syndrome when associated with impairment of glucose metabolism in case of the lack of a surgical indication. Recent experience suggests that the combination of different drugs may be able to control cortisol excess in a great majority of patients with CD.

Disulfiram sensitizes pituitary adenoma cells to temozolomide by regulating O6-methylguanine-DNA methyltransferase expression

O6-methylguanine-DNA methyltransferase (MGMT) activity is responsible for temozolomide (TMZ) resistance in patients harboring aggressive pituitary adenomas. Recently, disulfiram (DSF) has been shown to induce the loss of MGMT protein and increase TMZ efficacy in glioblastoma cells, while CD133+ nestin+ cells isolated from the cell population have been implicated as pituitary adenoma stem-like cells. However, whether DSF is able to potentiate the cytotoxic effects of TMZ on human pituitary adenoma cells has not been investigated to date. In the present study, CD133+ nestin+ phenotype cells were isolated from primary cultured human pituitary adenoma cells using microbeads. It was found that DSF reduced MGMT protein expression and sensitized human pituitary adenoma cells and stem-like cells to TMZ in vitro, while the proteasome inhibitor PS-341 abrogated the inhibitory effect of DSF on MGMT in vitro. The sensitizing effect of DSF was also verified in primary cultured human pituitary adenoma cells in vivo. The results of the present study suggested that DSF can increase the efficacy of the anti-tumor effect of TMZ on human pituitary adenoma cells and CD133+ nestin+ stem like cells via the ubiquitin-proteasomal MGMT protein elimination route. DSF combined with TMZ may be an effective therapeutic strategy against aggressive pituitary adenomas.

The role of temozolomide in the treatment of aggressive pituitary tumors

Pituitary tumors are amongst the most common intracranial neoplasms and are generally benign. However, some pituitary tumors exhibit clinically aggressive behavior that is characterized by tumor recurrence and continued progression despite repeated treatments with conventional surgical, radiation and medical therapies. More recently, temozolomide, a second generation oral alkylating agent, has shown therapeutic promise for aggressive pituitary adenomas and carcinomas with favorable clinical and radiographic responses. Temozolomide causes DNA damage by methylation of the O(6) position of guanine, which results in potent cytotoxic DNA adducts and consequently, tumor cell apoptosis. The degree of MGMT expression appears to be inversely related to therapeutic responsiveness to temozolomide with a significant number of temozolomide-sensitive pituitary tumors exhibiting low MGMT expression. The presence of high MGMT expression appears to mitigate the effectiveness of temozolomide and this has been used as a marker in several studies to predict the efficacy of temozolomide. Recent evidence also suggests that mutations in mismatch repair proteins such as MSH6 could render pituitary tumors resistant to temozolomide. In this article, the authors review the development of temozolomide, its biochemistry and interaction with O(6)-methylguanine-DNA methyltransferase (MGMT), its role in adjuvant treatment of aggressive pituitary neoplasms, and future works that could influence the efficacy of temozolomide therapy.

Temozolomide retreatment in a recurrent prolactin-secreting pituitary adenoma: Hormonal and radiographic response

BACKGROUND

Temozolomide is an oral alkylating agent with schedule-dependent antitumor activity against high-grade malignancies including high-grade glioma. Increasingly, reports have suggested that temozolomide may have activity as a salvage therapy for aggressive, recurrent pituitary adenomas or carcinomas that fail surgery, radiation and other pharmacotherapy. To our knowledge, temozolomide retreatment following initial responsiveness has not previously been demonstrated.

CASE REPORT

A woman was diagnosed with a prolactin-secreting pituitary adenoma in 1995 (age 44). Despite bromocriptine therapy, transphenoidal resection, radiotherapy, and cabergoline treatment she experienced continued clinico-radiographic progression, and temozolomide was initiated in 2011. She received three treatment cycles with rapid, dramatic clinico-radiographic response, and 99.3% reduction in serum prolactin. After three years of close observation, she developed recurrent radiographic progression and prolactin elevation. She was re-initiated on temozolomide, and after four cycles, clinical, radiographic and hormonal response was observed with a 92.2% reduction in serum prolactin.

CONCLUSIONS/SUMMARY

Temozolomide is an increasingly described treatment option for refractory pituitary adenomas and carcinomas. In the current report, we document rapid biochemical response following retreatment with temozolomide in aggressive pituitary adenoma. When "off label" salvage therapy with temozolomide is offered for patients with recurrent prolactinomas, retreatment at the time of recurrence can be considered.

Temozolomide Therapy for Aggressive Pituitary Tumors: Results in a Small Series of Patients from Argentina

We evaluated results of temozolomide (TMZ) therapy in six patients, aged 34-78 years, presenting aggressive pituitary tumors. In all the patients tested O(6)-methylguanine-DNA methyltransferase (MGMT) immunoexpression in surgical specimens was absent. Patients received temozolomide 140-320 mg/day for 5 days monthly for at least 3 months. In two patients minimum time for evaluation could not be reached because of death in a 76-year-old man with a malignant prolactinoma and of severe neutro-thrombopenia in a 47-year-old woman with nonfunctioning pituitary adenoma. In two patients (a 34-year-old acromegalic woman and a 39-year-old woman with Nelson's syndrome) no response was observed after 4 and 6 months, respectively, and the treatment was stopped. Conversely, two 52- and 42-year-old women with Cushing's disease had long-term total clinical and radiological remissions which persisted after stopping temozolomide. We conclude that TMZ therapy may be of variable efficacy depending on-until now-incompletely understood factors. Cooperative work on a greater number of cases of aggressive pituitary tumors should be crucial to establish the indications, doses, and duration of temozolomide administration.

Aggressive pituitary tumors

Pituitary adenomas are common intracranial tumors that are mainly considered as benign. Rarely, these tumors can exhibit an aggressive behavior, characterized by gross invasion of the surrounding tissues, resistance to conventional treatment leading to early and frequent recurrences. Even more rarely, pituitary tumors can give rise to cerebrospinal or systemic metastases qualifying as pituitary carcinomas according to the latest WHO definition. In the same classification, a subset of tumors with relatively distinct histopathological features was identified and defined as atypical adenomas designated to follow a more aggressive clinical course. This classification, although clinically useful, does not provide an accurate correlation between histopathological findings and the clinical behavior of these tumors, neither is it adequate to convey the precise features of 'aggressive' tumors. Thus, 'aggressive' pituitary adenomas need to be properly defined with clinical, radiological, histological and molecular markers in order to identify patients at increased risk of early recurrence or subsequent tumor progression. At present, no single marker or classification system of pituitary tumor aggressiveness exists, and clinically useful information in the literature is insufficient to guide diagnostic and therapeutic decisions. Treatment of patients with aggressive pituitary tumors is challenging since conventional treatments often fail, necessitating multiple surgical procedures with additional radiotherapy. Although traditional chemotherapy applied in other neuroendocrine tumors has not been shown to be efficacious, newer agents, particularly temozolomide, have shown promising results and are currently used despite the lack of data from a randomized prospective trial. Molecular targeted therapies such as mTOR and epidermal growth factor inhibitors have also been applied and might prove to be useful in the management of these patients. In the present review, we provide information regarding the epidemiology and clinical, histopathological and molecular features of aggressive pituitary tumors using recent employed definitions. In addition, we review currently employed therapeutic means providing a therapeutic algorithm and highlight the need to identify more specific disease-related and prognostic markers and the necessity for central registration of these tumors.

High response rates and prolonged survival in patients with corticotroph pituitary tumors and refractory Cushing disease from capecitabine and temozolomide (CAPTEM): a case series

BACKGROUND AND IMPORTANCE

Rarely, corticotrophic pituitary tumors take on an aggressive form characterized by rapid growth, invasion into local structures, compression of cranial nerves, and possible spread to distant sites. When conventional surgery, radiation therapy, and hormones fail to control progression and symptoms, alternative therapies are needed. A novel chemotherapeutic regimen of capecitabine and temozolomide (CAPTEM), originally designed in our laboratory, demonstrated dramatic antineoplastic effects against corticotrophic pituitary tumors.

CLINICAL PRESENTATION

We present a case series of 4 patients with aggressive, adrenocorticotrophic hormone--producing pituitary tumors who had previously depleted all surgical, radiation, and hormonal therapies and were then treated with CAPTEM. Dramatic clinical improvements in neurological deficits and Cushing symptoms were evident in all patients after treatment was initiated. Confirmed by radiographic imaging, 2 of 4 patients demonstrated complete regression of disease, 1 patient had a 75% regression, and the fourth patient has ongoing stable disease for > 4.5 years at the time of this writing. Immunohistochemical analysis of patients' tumor samples showed low O-methyguanyl methyltransferase expression and adequate levels of mismatch repair enzymes (MLH-1, MSH-2, MSH-6, and PMS-2), which are important for the in vivo efficacy of CAPTEM.

CONCLUSION

This is the first report of prolonged antitumor response to and radiographic complete remissions as a result of CAPTEM in patients with aggressive pituitary tumors who had exhausted all other therapies.

Treatment of pituitary carcinomas and atypical pituitary adenomas: a review

Atypical pituitary adenomas (APAs) are aggressive tumors, harboring a Ki-67 (MIB-1) staining index of 3% or more, and positive immunohistochemical staining for p53 protein, according to the World Health Organization (WHO) classification in 2004. Pituitary carcinomas (PC) usually develop from progressive APAs and predominantly consist of hormone-generating tumors, defined by the presence of disseminations in the cerebrospinal system or systemic metastases. Most of the cases with these malignant pituitary adenomas underwent surgeries, irradiations and adjuvant medical treatments, nevertheless, the therapies are mainly palliative. Recently, the efficacy of temozolomide (TMZ), an orally administered alkylating agent, has been reported as an alternative medical treatment. However, some recent studies have demonstrated a significant recurrence rate after effective response to TMZ. Further clinical and pathological researches of malignant pituitary adenomas will be required to improve the outcome of patients with these tumors.

Aggressive pituitary adenomas--diagnosis and emerging treatments

The WHO categorizes pituitary tumours as typical adenomas, atypical adenomas and pituitary carcinomas, with typical adenomas constituting the major class. However, the WHO classification does not provide an accurate correlation between histopathological findings and clinical behaviour. Tumours lacking typical histological features are classified as atypical, but not all are clinically atypical or exhibit aggressive behaviour. Pituitary carcinomas, by definition, have craniospinal or systemic metastases, although not all display classical cytological features of malignancy. Aggressive pituitary adenomas, defined from a clinical perspective, have earlier and more frequent recurrences and can be resistant to conventional treatments. Specific biomarkers have not yet been identified that can distinguish between clinically aggressive and nonaggressive pituitary adenomas, although the antigen Ki-67 proliferation index might be of value. This Review highlights the need to develop new biomarkers to facilitate the early detection of clinically aggressive pituitary adenomas and discusses emerging markers that hold promise for their identification. Defining aggressiveness is of crucial importance for improving the management of patients by enhancing prognostic predictions and effectiveness of treatment. New drugs, such as temozolomide, have potential use in the management of these patients; anti-VEGF therapy, mTOR and tyrosine kinase inhibitors are also potentially useful in managing selected patients.

Emerging drugs for acromegaly

INTRODUCTION

Acromegaly is a rare disease that severely impacts patients' health all the while, being a slowly progressing illness. In the past decades, advancements in treatment modalities, especially development of new drugs, as well as focused guidelines has improved management of acromegaly. Still, many patients are considered not sufficiently treated and there remains an ongoing need for further development.

AREAS COVERED

This article reviews new medical treatments currently under clinical investigation (such as pasireotide, oral octreotide and somatoprim) and under experimental development (such as octreotide implants, CAM2029 and ATL-1103).

EXPERT OPINION

As it seems unlikely that one single agent may achieve cure in 100% of cases, there is an urgent need for new agents that help patients where current medication fails. Imperatively, this means we have to improve our understanding of the underlying pathogenetic and molecular mechanisms.

Molecular status of pituitary carcinoma and atypical adenoma that contributes the effectiveness of temozolomide

There have been several reports of temozolomide (TMZ) treatment of pituitary carcinomas and atypical adenomas. O(6)-methyl-guanine-DNA methyltransferase is not the sole molecule determining the sensitivity to TMZ in pituitary carcinomas and atypical adenomas. The Japan Society of Hypothalamic and Pituitary Tumors study suggests that MSH6, one of mismatch repair pathway enzyme, fulfills a contributory role to the efficacy of TMZ treatment for pituitary carcinomas and atypical adenomas. The preserved MSH6 function might be essential for the responsiveness to TMZ treatment in pituitary carcinomas and atypical adenomas.

Management of large aggressive nonfunctional pituitary tumors: experimental medical options when surgery and radiation fail

Pituitary adenomas are generally considered benign tumors; however, a subset of these tumors displays aggressive behavior and are not easily cured. The protocol for nonsurgical treatment of aggressive pituitary lesions is less standardized than that of other central nervous system tumors. Aggressive surgical treatment, radiation, dopamine agonists, antiangiogenic drugs, and other chemotherapeutics all have roles in the treatment of aggressive pituitary tumors. More studies are needed to improve outcomes for patients with aggressive pituitary tumors.

ACTH-secreting Crooke cell carcinoma of the pituitary

PURPOSE

While pituitary adenomas are common, pituitary carcinomas are rare. It is unclear whether pituitary carcinomas arise de novo or evolve from adenomas.

METHODS

We studied the clinical characteristics and tissue samples from eight pituitary surgeries and the autopsy from a patient with pituitary carcinoma. A 16-year-old female patient was diagnosed with an aggressive Crooke cell macroadenoma. Following transsphenoidal surgery, clinical signs of Cushing disease quickly reappeared. During the 14-year course of the illness, eight pituitary surgeries, three courses of extracranial irradiation and two (90) Yttrium-DOTATOC treatments were undertaken. A bilateral adrenalectomy was performed. The patient died of metastatic disease and uncontrolled hypercortisolism due to an adrenal remnant. A systematic morphologic study (histologic staining, electron microscopy) of all available surgical and autopsy specimens was undertaken.

RESULTS

Brisk mitotic activity, high Ki-67 and p53 immunolabelling were present in the pituitary samples from the onset. High proportion of tumour cells showed irregular nuclei and large nucleoli, and gradual increase in MGMT staining was observed. The tumour remained of Crooke cell type throughout the course. Autopsy disclosed a postirradiation sarcoma in the pituitary area.

CONCLUSIONS

The question whether pituitary carcinomas arise de novo or transform from an adenoma cannot be answered at present with certainty.

Temozolomide responsiveness in aggressive corticotroph tumours: a case report and review of the literature

Pituitary carcinoma occurs in ~0.2% of resected pituitary tumours and carries a poor prognosis (mean survival <4 years), with standard chemotherapy regimens showing limited efficacy. Recent evidence suggests that temozolomide (TMZ), an orally-active alkylating agent used principally in the management of glioblastoma, may also be effective in controlling aggressive/invasive pituitary adenomas/carcinomas. A low level of expression of the DNA-repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) predicts TMZ responsiveness in glioblastomas, and a similar correlation has been observed in the majority of aggressive pituitary adenomas/carcinomas reported to date. Here, we report a case of a silent pituitary corticotroph adenoma, which subsequently re-presented with Cushing's syndrome due to functioning hepatic metastases. The tumour exhibited low immunohistochemical MGMT expression in both primary (pituitary) and secondary (hepatic) lesions. Initial TMZ therapy (200 mg/m² for 5 days every 28 days-seven cycles) resulted in marked clinical, biochemical [>50% fall in adrenocorticotrophic hormone (ACTH)] and radiological [partial RECIST (response evaluation criteria in solid tumors) response] improvements. The patient then underwent bilateral adrenalectomy. However, despite reintroduction of TMZ therapy (further eight cycles) ACTH levels plateaued and no further radiological regression was observed. We review the existing literature reporting TMZ efficacy in pituitary corticotroph tumours, and highlight the pointers/lessons for treating aggressive pituitary neoplasia that can be drawn from experience of susceptibility and evolving resistance to TMZ therapy in glioblastoma. Possible strategies for mitigating resistance developing during TMZ treatment of pituitary adenomas/carcinomas are also considered.

Temozolomide and unusual indications: review of literature

Temozolomide (TMZ) was first known to be useful as a radiosensitiser in both primary brain tumours like glioblastoma multiforme and oligodendroglioma. Later, TMZ proved its efficacy in the treatment of melanoma. Multiple publications have demonstrated the benefit of TMZ in terms of efficacy and tolerance (used as mono-therapy or as adjuvant chemotherapy) compared to the "gold standard" treatment of this kind of tumours. Furthermore, several recent clinical trials have shown the particular importance of TMZ in other types of cancer. This publication deals with the use of TMZ in cancers which are not formal indications for TMZ (excluding glioblastoma multiforme, oligodendroglioma and melanoma). It also includes a necessary review of recent literature about the role of TMZ in the treatment of brain metastases, lymphomas, refractory leukaemia, neuroendocrine tumours, pituitary tumours, Ewing's sarcoma, primitive neuroectodermal tumours, lung cancer and other tumours.

Temozolomide in the management of dopamine agonist-resistant prolactinomas

BACKGROUND

The majority of prolactinomas respond to dopamine agonist therapy, but a proportion are resistant, requiring other treatments including surgery and/or radiotherapy. Temozolomide is an oral chemotherapy agent, which has been used as a salvage therapy to treat aggressive pituitary adenomas and carcinomas, including prolactinomas, unresponsive to all conventional treatment.

CASE SERIES

We report three patients where temozolomide was used in the treatment of refractory prolactinomas. Case 1 describes a patient with a highly invasive prolactinoma, resistant to all conventional therapy, which responded dramatically to temozolomide used as a salvage treatment. In case 2, temozolomide was used after incomplete surgical resection to relieve chiasmal compression and avoid chiasm exposure to radiotherapy. In case 3, temozolomide enabled radiotherapy to be deferred in a 16-year old with a resistant prolactinoma. In all three cases, the tumours were negative by immunostaining for methylguanine methyltransferase (MGMT).

LITERATURE REVIEW AND DISCUSSION

A review of the published literature reveals 51 reported cases of temozolomide treatment for pituitary tumours, including 20 prolactinomas. Fifteen of the 20 prolactinomas showed a good response to temozolomide. Our analysis demonstrates a strong association between MGMT-negative staining and a good response to temozolomide (OR 9.35, P = 0.0030). Current clinical practice is to use temozolomide as a salvage therapy after all conventional modalities of treatment have failed. We suggest that, in selected cases, consideration should be given to using temozolomide earlier in the treatment algorithm.

Pituitary carcinomas and aggressive pituitary tumours: merits and pitfalls of temozolomide treatment

Pituitary carcinomas are rare, accounting for about 0.2% of all pituitary tumours. They represent a challenge to clinical practice in both diagnosis and treatment. They may present initially as typical pituitary adenomas, with a delayed appearance of aggressive signs, or as aggressive tumours from the outset. Predicting the pituitary tumour behaviour remains difficult: increased mitotic, Ki-67 and P53 indices might be associated with tumour aggression. The treatment of pituitary carcinomas and aggressive pituitary tumours includes surgery, adjuvant medical treatment, external beam radiotherapy and chemotherapy. Until recently, the treatment of pituitary carcinomas was mainly palliative and did not seem to increase overall survival. Recent case reports have detailed the successful use of temozolomide, an orally administered alkylating agent used to treat malignant gliomas, in the management of pituitary carcinomas and aggressive pituitary tumours. The outcome of treatment might depend on the expression of O(6)-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme that potentially interferes with drug efficacy. This review describes the clinical presentation and response to temozolomide in 44 patients with pituitary carcinomas or aggressive pituitary tumours reported in the literature. The results suggest that temozolomide should be considered a drug of major importance in the therapeutic algorithm of aggressive pituitary tumours and pituitary carcinomas. Because of the inconsistency of published data, MGMT expression should probably not be taken as a reason to deny these patients the potential benefit of temozolomide treatment, taking into account the paucity of other available treatments.

Failure of temozolomide and conventional doses of pegvisomant to attain biochemical control in a severe case of acromegaly

It has been suggested that treatment with adequate dose titration of pegvisomant, a GH antagonist, up to a maximum of 40 mg daily, can achieve IGF-1 normalisation in virtually all patients with acromegaly. On the other hand, temozolomide (TMZ), an alkylating cytostatic agent, has been reported to reduce pituitary tumour size and hormone hypersecretion in a small number of aggressive pituitary macroadenomas. In this paper we report the case of a patient resistant to very high doses of pegvisomant used in combination with somatostatin analogs (SSA) and to TMZ therapy. The patient, initially a 22 year-old man with an invasive GH-secreting pituitary macroadenoma (IGF-1, 371% upper limit of normal), had active acromegaly despite a repeat transsphenoidal surgery followed by radiotherapy and SSA (octreotide 800 μg sc daily) (IGF-1, 262% ULN). In combination with SSA, pegvisomant was started at 20 mg daily and doses were titrated up to 60 mg daily. IGF-1 was moderately reduced and stabilized at 200% ULN after 1 year of treatment. Serum pegvisomant level was 30,500 ng/l, the denaturalized GHBP concentration 1,120 pM and the endogenous GH level was 220 μg/l. Pegvisomant was stopped and TMZ therapy was given for 5 cycles. However, the patient reported an increase of acromegaly symptoms and the serum IGF-1 was raised to the same level prior to pegvisomant therapy. Consequently, pegvisomant was tried again with doses up to 100 mg daily finally resulting in normalisation of serum IGF-1 level and improvement of acromegaly symptoms and patient well-being. We conclude that in some patients with severe acromegaly refractory to multimodal therapy, biochemical control may be difficult to attain with conventional doses of pegvisomant or TMZ therapy.

Prolactinomas: diagnosis and treatment

Pituitary lactotrophs secrete prolactin. This process is enhanced by estrogen and inhibited by dopamine. Prolactinomas are benign neoplasms that rarely increase in size and are classified according to size as microadenomas (<10 mm diameter) or macroadenomas (>10 mm diameter). The clinical features of prolactinomas most commonly result from prolactin's effect on the gonads and breast in women and from mass effect in men. This review details the clinical features and management of patients with prolactinomas.

Temozolomide in aggressive pituitary adenomas and carcinomas

Temozolomide is an alkylating agent used in the treatment of gliomas and, more recently, aggressive pituitary adenomas and carcinomas. Temozolomide methylates DNA and, thereby, has antitumor effects. O6-methylguanine-DNA methyltransferase, a DNA repair enzyme, removes the alkylating adducts that are induced by temozolomide, thereby counteracting its effects. A Medline search for all of the available publications regarding the use of temozolomide for the treatment of pituitary tumors was performed. To date, 46 cases of adenohypophysial tumors that were treated with temozolomide, including 30 adenomas and 16 carcinomas, have been reported. Eighteen of the 30 (60%) adenomas and 11 of the 16 (69%) carcinomas responded favorably to treatment. One patient with multiple endocrine neoplasia type 1 and an aggressive prolactin-producing adenoma was also treated and demonstrated a good response. No significant complications have been attributed to temozolomide therapy. Thus, temozolomide is an effective treatment for the majority of aggressive adenomas and carcinomas. Evidence indicates that there is an inverse correlation between levels of O6-methylguanine-DNA methyltransferase immunoexpression and therapeutic response. Alternatively, high-level O6-methylguanine-DNA methyltransferase immunoexpression correlates with an unfavorable response. Here, we review the use of temozolomide for treating pituitary neoplasms.

Temozolomide (Temodar®) and capecitabine (Xeloda®) treatment of an aggressive corticotroph pituitary tumor

Only rarely do corticotroph pituitary tumors become invasive leading to symptoms caused by compression of cranial nerves and other local structures. When aggressive pituitary neuroendocrine tumors do develop, conventional treatment options are of limited success. A 50-year-old man developed a giant invasive corticotroph pituitary tumor 2 years after initial presentation. His tumor and symptoms failed to respond to maximal surgical, radio-surgical, radiation and medical therapy and a bilateral adrenalectomy was done. He subsequently developed rapid growth of his tumor leading to multiple cranial nerve deficits. He was administered salvage chemotherapy with capecitabine and temozolomide (CAPTEM), a novel oral chemotherapy regimen developed at our institution for treatment of neuroendocrine tumors. After two cycles of CAPTEM, his tumor markedly decreased in size and ACTH levels fell by almost 90%. Despite further decreases in ACTH levels, his tumor recurred after 5 months with increased avidity on PET scan suggesting a transformation to a more aggressive phenotype. Temozolomide had been reported to be effective against other pituitary tumors and this case adds to this literature demonstrating its use along with capecitabine (CAPTEM) against a corticotroph tumor. Further evaluation of the CAPTEM regimen in patients with pituitary neuroendocrine tumors which fail to respond to classic treatments is warranted.

Clinical review: Pituitary carcinoma: difficult diagnosis and treatment

CONTEXT

Although pituitary tumors are common, pituitary carcinoma is very rare and is only diagnosed when pituitary tumor noncontiguous with the sellar region is demonstrated. Diagnosis is difficult, resulting in delays that may adversely effect outcome that is traditionally poor. Barriers to earlier diagnosis and management strategies for pituitary carcinoma are discussed.

EVIDENCE ACQUISITION

PubMed was employed to identify relevant studies, a review of the literature was conducted, and data were summarized and integrated from the author's perspective.

EVIDENCE SYNTHESIS

The available data highlight the difficulties in diagnosis and management and practical challenges in conducting clinical trials in this rare condition. They suggest that earlier diagnosis with aggressive multimodal therapy may be advantageous in some cases.

CONCLUSIONS

Although pituitary carcinoma remains difficult to diagnose and treat, recent developments have led to improved outcomes in selected cases. With broader use of molecular markers, efforts to modify current histopathological criteria for pituitary carcinoma diagnosis may now be possible. This would assist earlier diagnosis and, in combination with targeted therapies, potentially improve long-term survival.

MGMT immunoexpression in adamantinomatous craniopharyngiomas

At present, no effective medical treatment exists for recurrent and aggressive craniopharyngiomas that are resistant to conventional therapies, including surgery and adjuvant radiotherapy. Temozolomide is an alkylating chemotherapeutic agent used routinely in the management of high grade gliomas. The response to temozolomide is suggested to be dependent on the tumoral expression of O-6 methylguanine DNA methyltransferase (MGMT). Evidence supports that low MGMT immunoexpression correlates with positive response to temozolomide. Therefore, we aimed to assess MGMT immunoexpression in adamantinomatous craniopharyngiomas, in an effort to predict the likelihood of response to temozolomide. The MGMT immunostaining was performed on 23 adamantinomatous craniofaryngiomas operated at the Sisli Etfal Training and Research Hospital and identified by histological analysis. Paraffin embedded tissue sections were immunostained for MGMT and were evaluated semi-quantitatively. Of the 23 cases evaluated, 22 (96%) demonstrated negative (<10%) and 1 (4%) demonstrated low (10%) MGMT immunoexpression. Data from this study suggest a high proportion of adamantinomatous craniopharyngiomas exhibit negative/low MGMT immunoreactivity and could be treated with temozolomide, if conventional therapy fails.

A mechanism of acquiring temozolomide resistance during transformation of atypical prolactinoma into prolactin-producing pituitary carcinoma: case report

BACKGROUND AND IMPORTANCE

The case presented here describes the clinical evolution of a pituitary carcinoma from an atypical prolactinoma after temozolomide (TMZ) treatment. The mechanism of acquisition of TMZ resistance was analyzed.

CLINICAL PRESENTATION

A 60-year-old woman with atypical prolactinoma had been treated for 7 years with multiple therapies, including dopamine agonists, surgical intervention (5 times), conventional radiotherapy, and radiosurgery. The patient deteriorated as a result of tumor enlargement. Ten cycles of TMZ therapy, 200 mg/m for 5 days every 4 weeks, improved the patient's performance status and caused tumor shrinkage. Six months after discontinuation of TMZ, the tumor progressed into pituitary carcinoma with tumor regrowth and intraventricular dissemination. TMZ therapy was ineffective this time. A sixth surgery and salvage chemotherapy failed to improve the patient's condition, and she died 9 years after the first diagnosis. Throughout the treatment course, O6-methyl-guanine-DNA methyltransferase (MGMT) was immunonegative in the tumor specimens, including the TMZ-refractory pituitary carcinoma. Mutation of p53 was identified in both the atypical prolactinoma and pituitary carcinoma. In contrast, major differences were noted for mismatch repair protein MSH6 immunostaining: Although MSH6 was diffusely immunopositive in the atypical adenoma, it became immunonegative when the tumor evolved into TMZ-refractory pituitary carcinoma.

CONCLUSION

Loss of MSH6 occurred during the progression from an atypical prolactinoma to a pituitary carcinoma, which may have caused resistance to TMZ treatment. This case suggests that preserving MSH6 function is essential for responsiveness to TMZ treatment in MGMT-negative and p53-mutated atypical pituitary adenoma or pituitary carcinoma.

Aggressive pituitary tumours: the role of temozolomide and the assessment of MGMT status

BACKGROUND

Aggressive pituitary tumours are associated with substantial morbidity and mortality. Treatment options are often limited, and chemotherapy has been reserved as salvage therapy although historically results have often been disappointing. However, temozolomide, an oral alkylating agent, has recently demonstrated significant activity against these tumours. A DNA repair protein, 06-methylguanine-DNA methyltransferase (MGMT) has been suggested as a biomarker to predict response to temozolomide in pituitary tumours.

MATERIALS AND METHODS

This paper will review the current literature on temozolomide and pituitary tumours and discuss the recent controversy surrounding the value of determining the MGMT status in this tumour group. A PubMed search was performed to retrieve articles, using the terms 'pituitary tumour' and 'temozolomide'.

RESULTS

Overall, 24/40 (60%) of the published cases demonstrated a response to temozolomide therapy. The highest response rates were seen amongst prolactinomas (73%) and ACTH-secreting tumours (60%), whilst nonfunctioning pituitary tumours exhibit lower response rates (40%). Responsivity is typically evident in the first 3 months of therapy and may be dramatic and sustained. Low MGMT expression, as determined by immunohistochemistry, is associated with a high response rate (76%), whilst high MGMT expression has not been associated with responses. MGMT promoter methylation does not correlate with temozolomide response.

CONCLUSIONS

Temozolomide is the first chemotherapeutic agent to show substantial response rates in aggressive pituitary tumours. MGMT immunohistochemistry, but not MGMT methylation analysis, shows promise as a predictive tool. Prospective clinical trials are now necessary to more accurately determine the efficacy of this agent in this patient group.

MGMT immunoexpression in growth hormone-secreting pituitary adenomas and its correlation with Ki-67 labeling index and cytokeratin distribution pattern

Recent publications suggest the utility of temozolomide (TMZ) in the management of aggressive pituitary adenomas and carcinomas, resistant to conventional treatments. The response to TMZ is inversely correlated with tumoral expression of O-6 methylguanine DNA methyl transferase (MGMT). Therefore, we aimed to assess MGMT immunoexpression in pure GH-secreting pituitary adenomas, in an effort to predict the likelihood of response to TMZ, and to correlate MGMT immunoexpression with Ki-67 LI and cytokeratin (CK) distribution pattern. Our material consisted of 36 GH-secreting pituitary adenomas (21 female,15 male, mean age 42.5±10.5), operated at our center between 2003 and 2010. Immunostaining for MGMT, Ki-67, and CK was performed using avidin-biotin-peroxidase complex method. Immunoreactivity for MGMT and Ki-67 was evaluated microscopically and recorded as percentages of positive nuclear immunostaining. CK distribution pattern was also evaluated microscopically and assoreted into dot-like and nondot-like pattern subtypes. MGMT immunoexpression scored as 0=none, 1=<10%, 2=<25%, 3=<50%, and 4=>50%. Staining for MGMT was <10% (score 1) in 30 (83.3%), 10-25% (score 2) in 3 (8.3%), 25-50% (score 3) in 2 (5.6%) and >50% (score 4) in 1 (2.8%) of the tumors, respectively. There was no correlation between Ki-67 LI and CK distribution pattern with MGMT immunoreactivity (P>0.05). Data from the current study suggest a large proportion of GH-secreting adenomas, including those with dot-like CK distribution pattern and high Ki-67 LI, demonstrate negative/low MGMT immunoreactivity and could be treated with TMZ, if conventional treatment fails.

Resistant prolactinomas

Prolactinomas are the most common hormonally active pituitary tumors and are usually successfully treated with dopamine agonists. A small proportion, however, appears not to respond to such treatment and such cases are termed resistant prolactinomas. Resistance is generally defined as failure to achieve normoprolactinemia and inability to induce tumor shrinkage. Reduced dopamine receptor density on lactotroph cells is currently considered the major underlying mechanism of resistance. Treatment options in resistant cases usually include substitution with another dopamine agonist, increasing the dose of the drug, as well as surgery, radiotherapy, and experimental medical therapies.

Therapy of aggressive pituitary tumors

INTRODUCTION

Aggressive tumors of the pituitary gland are classically defined as pituitary tumors with a massive invasion of the surrounding anatomical structures and rapid growth. They are notoriously difficult to manage and are associated with poor prognosis because the therapeutic options are limited and the tumors are generally unresponsive to therapy.

AREAS COVERED

This review focuses on treatment options for aggressive pituitary tumors, including surgery, radiotherapy and medical treatment, as well as focusing on the promising therapeutic options for aggressive pituitary tumors, evaluating the literature of the last 15 years. With the exception of prolactinomas, surgery is the first-line option, but most aggressive pituitary tumors often require repeated surgery. Pharmacotherapies are useful when surgery is unlikely to improve symptoms, or as an adjunct therapy to surgery. In prolactinomas, dopamine agonists are the first-line treatment and normalize prolactin levels in most patients, even those with macroprolactinomas. Somatostatin analogs are effective agents for primary therapy, pre-operatively or post-operatively to control tumor re-expansion of pituitary adenomas. However, dopamine agonists and somatostatin analogs are not as effective as they are for the treatment of non-aggressive adenomas. When surgery and pharmacotherapy fail, radiotherapy is a useful third-line strategy. Conventional chemotherapy is poorly effective but recent case reports with the temozolomide, an alkylating agent, have provided better results in the short term.

EXPERT OPINION

Aggressive pituitary tumors are associated with poor prognosis as therapeutic options are limited. Moreover, they tend to recur quickly after initial treatment, are generally unresponsive to therapy, and are difficult to manage. To improve the overall response rate, the early application of current therapeutic approaches with the incorporation of new therapeutic developments is mandatory.

Temozolomide for corticotroph pituitary adenomas refractory to standard therapy

To highlight the potential of temozolomide (TMZ) to induce rapid tumor regression in patients with aggressive corticotroph adenomas (CA) that are refractory to surgery and radiation therapy and to review use of TMZ in other pituitary tumors. We present a case of a 56-year-old male with a 3 cm CA treated with transphenoidal surgery (TSS) and conventional radiotherapy in the same year. His hypercortisolemia recurred 11 years later with rapid tumor growth (to 4.2 × 2.5 cm) and he underwent a second TSS with good resection. The tumor recurred 6 months later with ophthalmoplegia. Over 16 months he underwent an additional three surgeries (two TSS, one craniotomy) and repeated conventional radiotherapy. Ki67 staining index on surgical specimens was 5-6%. Temozolomide is an oral alkylating agent approved for glioblastoma multiforme treatment that has only recently shown promise in treating some pituitary tumors. In this patient TMZ was started at 150 mg/m²/day, titrated to 200 mg/m²/day, taken 5 days per month. The only significant side effect was moderate nausea. After 10 weeks, the tumor showed a remarkable 60% regression with objective improvement in ophthalmoplegia. Treatment of aggressive CAs represents a therapeutic challenge and in some cases surgical debulking and radiotherapy are of limited success. Few reports of CAs responsive to TMZ have been reported in the literature. To our knowledge, this case represents the most rapid robust CA shrinkage response reported to date. Further randomized clinical trials of TMZ in the treatment of aggressive pituitary adenomas are warranted.

Temozolomide-induced inhibition of pituitary adenoma cells

Object

Aggressive pituitary adenomas frequently require multimodality treatment including pituitary-suppressive medications, microsurgery, and radiation therapy or radiosurgery. The effectiveness of temozolomide in terms of growth suppression and decreased hormonal production is evaluated.

Methods

Three pituitary adenoma cell lines—MMQ, GH3, and AtT20—were used. A dose escalation of temozolomide was performed for each cell line, and inhibition of cell proliferation was assessed using an MTT assay. Concentrations of temozolomide that produced statistically significant inhibition of cell proliferation for each cell type were identified. Extent of apoptosis for each selected temozolomide concentration was studied using TUNEL staining. The effect of temozolomide on prolactin secretion in MMQ and GH3 cells was also measured via ELISA.

Results

Significant inhibition of cell proliferation was noted for MMQ and GH3 cells at a concentration of 250 μM temozolomide. The AtT20 cells demonstrated statistically significant cell inhibition at a concentration of only 50 μM temozolomide (p < 0.05). Apoptosis significantly increased in all cell lines in as little as 24 hours of incubation at the respective temozolomide concentrations (p < 0.05). Prolactin secretion in the prolactin secreting MMQ and GH3 cell lines was inhibited by 250 μM temozolomide.

Conclusions

Temozolomide inhibits cell proliferation and induces apoptotic cell death in aggressive pituitary adenoma cells. A reduction in hormonal secretion in prolactinoma cells was also afforded by temozolomide. Temozolomide may prove useful in the multimodality management of aggressive pituitary adenomas.

Dopamine agonist-resistant prolactinomas

The authors' object in this paper was to review the definition, epidemiology, biology, resistance mechanisms, and treatment options for dopamine agonist-resistant prolactinomas (DARPs). Prolactinomas are relatively unique among primary brain tumors in that medical treatment alone using dopamine agonists carries a high probability of disease control or even radiographic and endocrine remission, and thus has replaced surgery as the first line of therapy. Unfortunately, slightly less than 10% of patients with prolactinomas do not experience normalization of their prolactin levels in response to dopamine agonists, and harbor tumors that are resistant to dopamine agonist therapy. A literature review underscores that in male patients these DARPs are more likely to be invasive macroadenomas than dopamine agonist-responsive prolactinomas and that they are also more angiogenic, more proliferative, and more likely to exhibit cellular atypia. Estrogen receptor antagonists and temozolomide are the most commonly applied medical therapies in cases in which resection and radiosurgery have not induced remission of the hyperprolactinemia. Dopamine agonist-resistant prolactinomas exhibit aggressive behavior and tend to be large, invasive, hyperangiogenic tumors with high mitotic indices, which makes their management via surgery, radiosurgery, or alternative medical therapies challenging, thus underscoring the need for novel medical therapies or treatment regimens that target these lesions.

HER2/ErbB2 receptor signaling in rat and human prolactinoma cells: strategy for targeted prolactinoma therapy

Dopamine agonist resistance or intolerance is encountered in approximately 20% of prolactinoma patients. Because human epidermal growth factor receptor 2 (HER2)/ErbB2 is overexpressed in prolactinomas and ErbB receptor ligands regulate prolactin (PRL) gene expression, we tested the role of HER2/ErbB2 in prolactinoma hormone regulation and adenoma cell proliferation to assess the rationale for targeting this receptor for prolactinoma therapy. As we showed prolactinoma HER2 overexpression, we generated constitutively active HER2-stable GH3 cell transfectants (HER2CA). PRL mRNA levels were induced approximately 250-fold and PRL secretion was enhanced 100-fold in HER2CA cells, which also exhibited increased proliferation. Lapatinib, a dual tyrosine kinase inhibitor (TKI) of both epidermal growth factor receptor (EGFR)/ErbB1 and HER2, blocked receptor signaling, and suppressed PRL expression more than gefitinib, a TKI of EGFR/ErbB1. Lapatinib also suppressed colony formation in soft agar more than gefitinib. Oral lapatinib treatment caused tumor shrinkage and serum PRL suppression both in HER2CA transfectant-inoculated Wistar-Furth rats and in estrogen-induced Fischer344 rat prolactinomas. In cultured human cells derived from resected prolactinoma tissue, lapatinib suppressed both PRL mRNA expression and secretion. These results demonstrate that prolactinoma HER2 potently induces PRL and regulates experimental prolactinoma cell proliferation. Because pituitary HER2 signaling is abrogated by TKIs, this receptor could be an effective target for prolactinoma therapy.