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Endocrine Oncology, Pituitary Disorders
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Temozolomide in the Treatment of Aggressive Pituitary Tumours – An Overview of Existing Knowledge and Future Perspectives

Published Online: September 12th 2012 European Endocrinology, 2012;8(2):116-121 DOI: http://doi.org/10.17925/EE.2012.08.02.116
Authors: Ann McCormack
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Abstract:
Overview

The management of aggressive pituitary tumours remains a challenge, however, the recent identification of temozolomide as a chemotherapeutic agent with significant efficacy against these tumours has heralded a new therapeutic era. There has been an exponential growth in the international experience with temozolomide over the past five years, now totalling 50 published cases. Overall, 67 % of cases demonstrated a response to temozolomide. Prolactin- and adrenocorticotrophic hormone (ACTH)-secreting tumours respond more frequently than non-functioning tumours. Response is typically evident in the first three months of treatment. Adverse effects occur in almost half of patients, although the majority are mild. The expression of a DNA repair enzyme, 06-methylguanine-DNA methyltransferase (MGMT), as determined by immunohistochemistry, appears to be the primary determinant of response to temozolomide in pituitary tumours. There is suggestion that MGMT may also play a role in pituitary tumorigenesis. Over the next few years we will see temozolomide used earlier in the treatment algorithm of aggressive pituitary tumours, making it imperative to collect global long-term data on its use.

Keywords

Pituitary tumour, pituitary carcinoma, temozolomide, MGMT

Article:

Pituitary tumours are common, with an estimated prevalence of 16.7 % in the general population based on imaging and autopsy studies.1 Clinically significant pituitary tumours are more prevalent than previously recognised, with one case per 1,000–1,300 people.2,3 The majority of pituitary tumours are indolent, slow-growing neoplasms. However, 40–50 % of pituitary tumours are locally invasive and commonly unable to be completely surgically excised.4,5 An ‘aggressive pituitary tumour’ typically refers to an invasive pituitary tumour that demonstrates progressive growth despite multimodal therapy, including surgery and radiotherapy. Whilst these tumours have malignant potential, the term pituitary carcinoma is strictly reserved for those tumours with demonstrated craniospinal or systemic metastases.6 As there is a lack of formal criterion used to define an aggressive pituitary tumour, epidemiological data with respect to this group is lacking. The World Health Organization pathological classification of an ‘atypical pituitary adenoma’ (Ki67 >3 %, excessive p53 immunoreactivity and increased mitotic activity) was coined in an attempt to identify a tumour with the potential for more aggressive behaviour.7 A recent study, conducted in a tertiary referral centre, identified 15 % of atypical adenomas amongst their surgical cohort.8 Pituitary carcinoma is rare, accounting for 0.2 % of pituitary tumours.9

The management of aggressive pituitary tumours is challenging, and there is substantial morbidity and mortality associated with both the tumour and treatment. Patients often undergo multiple surgeries and radiotherapy in an attempt to control tumour growth. These tumours are often also resistant to medical therapies, such as dopamine agonists. Historically, systemic chemotherapy was reserved as a ‘last resort’ therapy, principally due to the lack of identification of a consistently effective chemotherapeutic agent. However, over the past five years temozolomide, an oral alkylating agent commonly used in the management of glioblastoma, has emerged as the first chemotherapeutic with substantial efficacy in the treatment of aggressive pituitary tumours. International experience with temozolomide, as used in the management of an aggressive pituitary tumour, has grown exponentially, with 50 published cases now reported. This review will summarise and examine the existing knowledge base, but also speculate on the future possibilities regarding the use of temozolomide in pituitary tumours. The role of 06-methylguanine-DNA methyltransferase (MGMT), a DNA repair protein, as a biomarker of response to temozolomide and its possible role in pituitary tumour biology will be discussed.

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Article Information:
Correspondence

Ann McCormack, Department of Endocrinology, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia. E: a.mccormack@garvan.org.au

Received

2012-07-02T00:00:00

References

  1. Ezzat S, Asa SL, Couldwell WT, et al., The prevalence of pituitary adenomas: a systematic review, Cancer, 2004;101:613–9.
  2. Daly AF, Rixhon M, Adam C, et al., High prevalence of pituitary adenomas: a cross-sectional study in the province of Liege, Belgium, J Clin Endocrinol Metab, 2006;91:4769–75.
  3. Fernandez A, Karavitaki N, Wass JA, Prevalence of pituitary adenomas: a community-based, cross-sectional study in Banbury (Oxfordshire, UK), Clin Endocrinol (Oxf), 2010;72:377–82.
  4. Kaltsas GA, Nomikos P, Kontogeorgos G, et al., Clinical review: Diagnosis and management of pituitary carcinomas, J Clin Endocrinol Metab, 2005;90:3089–99.
  5. Sautner D, Saeger W, Invasiveness of pituitary adenomas, Pathol Res Pract, 1991;187:632–6.
  6. Scheithauer BW, Kovacs KT, Laws ER Jr, Randall RV, Pathology of invasive pituitary tumors with special reference to functional classification, J Neurosurg, 1986;65:733–44.
  7. Lloyd RV, Kovacs K, Young WF, Pituitary Tumors, in: DeLellis RA, Lloyd RV, Heitz PU, Eng C (eds), World Health Organization Classification of Tumours, Pathology and Genetics of Tumours of Endocrine Organs, Lyon: IARC Press: 2004;10–47.
  8. Zada G, Woodmansee WW, Ramkissoon S, et al., Atypical pituitary adenomas: incidence, clinical characteristics, and implications, J Neurosurg, 2011;114:336–44.
  9. Pernicone PJ, Scheithauer BW, Sebo TJ, et al., Pituitary carcinoma: a clinicopathologic study of 15 cases, Cancer, 1997;79:804–12.
  10. Neyns B, Tosoni A, Hwu WJ, Reardon DA, Dose-dense temozolomide regimens: antitumor activity, toxicity, and immunomodulatory effects, Cancer, 2010;116:2868–77.
  11. Marchesi F, Turriziani M, Tortorelli G, et al., Triazene compounds: mechanism of action and related DNA repair systems, Pharmacol Res, 2007;56:275–87.
  12. Kaina B, Ziouta A, Ochs K, Coquerelle T, Chromosomal instability, reproductive cell death and apoptosis induced by O6-methylguanine in Mex-, Mex+ and methylation-tolerant mismatch repair compromised cells: facts and models, Mutat Res, 1997;381:227–41.

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