Therapeutic implications of accurate classification of pituitary adenomas

Recent data suggest that 1 of 5 individuals in the general population is affected with a pituitary adenoma. Many of these neoplasms are clinically non-functioning adenomas that may be small and clinically undetected or may present as mass lesions; others are hormonally active and cause significant morbidity due to the metabolic effects of hormone excess (e.g., acromegaly and cushing's disease). In either case, they can grow and invade adjacent anatomic structures. Tumors with similar clinical features are morphologically heterogenous and detailed comprehensive classification of pituitary adenomas is important to predict specific clinical behaviors and genetic changes that serve as targets for therapy. We provide a practical approach to clinical diagnosis and highlight the pitfalls in the classification of these common neoplasms.     

Correlation between SPARC (Osteonectin) expression with immunophenotypical and invasion characteristics of pituitary adenomas

Pituitary adenomas are the third most common intracranial tumors. Invasive adenomas account for only 0.1–0.2% of pituitary tumors. SPARC is a matrix glycoprotein that plays a role in progression and invasiveness of neoplasms. In this study, we examined the potential role of SPARC in invasive pituitary adenomas. Forty pituitary adenomas have been examined with histopathological and immunohistochemical techniques. The cohort has been classified into two groups as invasive (n = 25) and non‐invasive (n = 15) utilizing the Hardy classification. Formalin fixed tissues have been stained with hematoxylin eosin. Ki‐67, p53, and SPARC monoclonal antibodies have been used. We did not detect any significant difference on Ki‐67, SPARC, and p53 expression patterns correlating with the pathological subtype or invasiveness. Only 24% of invasive adenomas had Ki‐67 levels over 1%. A total of 67.7% non‐invasive adenomas had Ki‐67 levels below 1%. We did not detect any relation between SPARC levels and invasiveness of pituitary adenomas. Absence of significant SPARC expression in tumor progression, sellar dilatation, erosion and destruction suggest that SPARC scores are not related with invasiveness or progressiveness of pituitary adenomas.     

Plurihormonal pituitary adenomas: immunostaining of all pituitary hormones is mandatory for correct classification

AIMS: We studied the clinicopathological characteristics of plurihormonal pituitary adenomas. METHODS AND RESULTS: The study material included 167 plurihormonal adenomas, which consisted of 31% of the surgically removed pituitary adenomas that we collected during a 12-year period. The mean age of patients with plurihormonal adenoma was 45.7 years (range 13-75 years). There were 86 men and 81 women. All tumours were fully classified by immunohistochemical staining for seven pituitary hormones or subunits. Thirty immunohistochemical subtypes of plurihormonal adenomas were recognized. Hormonal symptoms were present in 70% of patients, while serum hormonal levels were increased in 89% of patients. Most patients had symptoms related to only one of the hormones and only 7% of patients had symptoms related to two hormones. The most common hormonal symptom was acromegaly (50%); symptoms related to hyperprolactinaemia ranked second (20%). Double immunostaining of all the possible combinations of the hormones was performed in 30 selected tumours, and they all showed mixtures of hormones in individual adenoma cells in any hormonal combinations studied. The latter finding supported the view that plurihormonal adenomas are monomorphous adenomas. CONCLUSIONS: Plurihormonal adenomas are common pituitary adenomas. Immunohistochemical staining of all pituitary hormones is mandatory for correct classification.     

Clinicopathologic features of familial pituitary adenomas

Pituitary adenomas are common neoplasms. Initially considered as sporadic tumours, some of them are associated with familial syndromes such as familial isolated pituitary adenoma, multiple endocrine neoplasia type 1 and type 4, X-linked acrogigantism syndrome, Carney complex, pheochromocytoma/paraganglioma–pituitary adenoma, pituitary blastoma and McCune–Albright syndrome. They represent a group of diseases with different genetic background and variable phenotype. Here, we summarize the clinicopathological features of pituitary adenomas associated with these familial syndromes.     

Pituitary tumors in the elderly

The present study was designed to investigate the incidence and immunohistochemical characteristics of pituitary tumors in the elderly. In our surgical collection of 1925 cases, we examined tumor tissue from 15 patients over 80 years of age. Pituitaries obtained at routine autopsies from 692 subjects over 80 years of age were also investigated. Of the 15 surgical cases studied, the majority of patients presented with chiasmatic syndromes, likely caused by macroadenomas. Gonadotroph adenomas were the most frequently diagnosed tumor type, followed by null-cell adenomas and oncocytomas. There is only one case with GH cell adenoma. Among 692 autopsy cases, 79 (11.4%) pituitaries were found to contain adenomas in the anterior lobe. In one pituitary, two separate adenomas were detected, hence the number of adenomas in our material was 80. All autopsy cases were microadenomas except one. The mean diameter of adenomas was 2.2 mm. ACTH cell adenomas were the most frequently diagnosed tumor type, followed by PRL cell adenomas and null cell adenomas. The occurrence of pituitary adenomas discovered after routine autopsy in the elderly was common, although these tumors were not found frequently in surgical cases over 80 years of age. Our immunohistochemical study revealed that many tumors contained one or more than one anterior pituitary hormone, although almost all pituitary adenomas were considered to be clinically inactive in surgical and autopsy cases.     

Ultrastructural Markers in the Pathologic Diagnosis of Pituitary Adenomas

The functional-morphologic classification of pituitary adenomas increased the number of distinguishable morphologic entities from 3 (acidophilic, basophilic, chromophobic) to 15. Identification of tumor types requires histology as well as im-munohistochemistry and electron microscopy. Electron microscopy has a pivotal role in the recognition and separation of entities with overlapping immunohistochemical profiles. Electron microscopic diagnosis is facilitated considerably by structural markers present in the majority of adenoma types. Two groups of ultrastructural markers are discussed. Organelle markers are represented by specific morphology/arrangement of ubiquitous cytoplasmic constituents (rough endoplasmic reticulum, Golgi apparatus, mitochondria). Special markers are usually restricted to a particular pituitary cell type, its tumors, or both (filamentous aggregates, particular morphology of secretory granules, etc). Evaluation of general ultrastructural features and identification of structural markers permit conclusive diagnosis in the majority of pituitary adenomas. Cell derivation remains uncertain in many so-called clinically nonfunctioning adenomas with no or insufficient markers and poorly developed cytoplasmic organization associated with low endocrine activity.     

A classification tree approach for pituitary adenomas

It is difficult to evaluate the recurrence and progression potential of pituitary adenomas at presentation. The World Health Organization classification of endocrine tumors suggests that invasion of the surrounding structures, size at presentation, an elevated mitotic index, a Ki-67 labeling index higher than 3%, and extensive p53 expression are indicators of aggressive behavior. Nevertheless, Ki-67 and p53 labeling index evaluation is subject to interobserver variability, and their cutoff values are controversial. In the present study, the prognostic value of Ki-67 and p53 protein labeling indices and their correlation with clinical and radiologic parameters were evaluated using digital image analysis in a series of 166 pituitary adenomas in patients having undergone a follow-up of at least 6 years to evaluate the impact on the recurrence and progression potential of pituitary adenomas. The data were analyzed using the receiver operating characteristic curve and classification and regression tree analysis. The results showed that, in the unstratified data set, the commonly used threshold of the Ki-67 index of 3% has a high specificity (89.5%) but a low sensitivity (53.8%). Unsatisfactory performance results were obtained by performing receiver operating characteristic curve analysis on the p53 labeling index. On the contrary, the classification and regression tree analysis-derived tree demonstrated that each pituitary adenoma subtype has specific prognostic factors. Specifically, the Ki-67 labeling index is a useful prognostic factor in nonfunctioning, adrenocorticotropin, and prolactin adenomas, but with different thresholds. In conclusion, our study emphasizes that the term pituitary adenomas includes different types of tumors, each one having specific prognostic factors.     

Molecular Pathology of the Pituitary Adenomas

Molecular techniques have been applied to the study of pituitary adenomas by many investigators. We have used nonisotopicin situ hybridization (ISH) to analyze pituitary adenomas in our laboratory. These studies have provided insight into mRNA production by various adenomas, and have contributed toward our new proposed clinical and cytofunctional classification of pitutiary adenomas. Presented in part at the Molecular Endocrine Pathology Symposium at the International Academy of Pathology XXI International Congress, Budapest, Hungary, October 20–25, 1996.     

My approach to pathology of the pituitary gland

The sellar region is the site of a large number of pathological entities arising from the pituitary and adjacent anatomical structures, including brain, blood vessels, nerves and meninges. The surgical pathology of this area requires the accurate identification of neoplastic lesions, including pituitary adenoma and carcinoma, craniopharyngioma, neurological neoplasms, germ cell tumours, haematological malignancies and metastases, as well as non-neoplastic lesions such as cysts, hyperplasias and inflammatory disorders. This review provides a practical approach to the diagnosis of pituitary specimens that are sent to the pathologist at the time of surgery. The initial examination requires routine haematoxylin and eosin staining to establish whether the lesion is a primary adenohypophysial proliferation or one of the many other pathologies that occurs in this area. The most common lesions resected surgically are pituitary adenomas. These are evaluated with several special stains and immunohistochemical markers that are now available to accurately classify these pathologies. The complex subclassification of pituitary adenomas is now recognised to reflect specific clinical features and genetic changes that predict targeted treatments for patients with pituitary disorders.     

Ultrastructural Morphology of Folliculo-Stellate Cells in Human Pituitary Adenomas

Fifty-six pituitary adenomas were studied by electron microscopy in a search for the presence of folliculo-stellate cells (FSCs) with the aim of evaluating their prevalence and ultrastructural morphology. FSCs were scattered in two adenomas (one oncocytoma and one densely granulated GH cell adenoma) and were numerous in a sparsely granulated GH cell adenoma; their overall prevalence was 5.4%. Ultrastructural examination of the three neoplasms revealed that FSCs were hypertrophic element with abundant cytoplasm and organelles (in contrast to FSCs of the normal pituitary) and no obvious signs of neoplastic transformation. Junctional complexes between FSCs were similar to those described in the normal gland. Numerous follicular structures were lined by FSCs. FSCs in pituitary adenomas are probably nonneoplastic, reactive cells showing signs of hyperactivity, similar to FSCs found during pituitary hypersecretion and in estrogen-induced tumor.     

Analysis of Cox-2 and thromboxane synthase expression in pituitary adenomas and carcinomas

Recent studies have examined the role of cyclooxygenase-2 (Cox-2) expression in normal pituitaries and pituitary adenomas and have suggested a role for Cox-2 in the regulation of angiogenesis in the pituitary. Thromboxane synthase (TBXAS), which catalyzes the synthesis of thromboxane A2, is one of the downstream enzymes in Cox metabolism and appears to play a role in the regulation of invasiveness and angiogenesis in some neoplasms. To analyze the role of Cox-2 and TBXAS in pituitary tumor progression, we examined normal pituitaries (n = 8), pituitary adenomas (n = 174), and pituitary carcinomas (n = 7) for expression of Cox-2 and TBXAS by immunohistochemistry. Weak Cox-2 and moderate TBXAS expression was present in normal pituitary cells. Most pituitary adenomas showed increased expression of both Cox-2 and TBXAS. Pituitary tumors as a whole, but particularly carcinomas, showed greater Cox-2 expression than did normal pituitaries. Pituitary adenomas and carcinomas also showed greater staining for TBXAS when compared to normal pituitary. Nonfunctional adenomas had significantly higher levels of TBXAS expression compared to functional adenomas (p = 0.017). Adenomas and carcinomas showed similar degrees of staining for TBXAS. In summary, TBXAS appears to be one of the up-regulated downstream enzymes of Cox metabolism in pituitary tumors. Both Cox-2 and TBXAS may play an important role in pituitary tumor development and progression.     

Histologic and immunohistochemical study of clinically non-functioning pituitary adenomas

Seventy-five clinically non-functioning pituitary adenomas were characterized in terms of their histologic and immunohistochemical features. Fourteen adenomas (18.7%) were positive for hormones other than gonadotropins. These included two somatotroph adenomas, three lactotroph adenomas, four thyrotroph adenomas, four corticotroph adenomas and one unusual plurihormonal adenoma. Fifty-five adenomas (73.3%) were exclusively positive for one or more gonadotropin subunits (β-follicle stimulating hormone, p-luteinizing hormone, and α-subunit of glycoprotein hormones), but negative for other hormones such as growth hormone and β-thyrotropin. Histologically, a papillary arrangement along the capillary was most characteristically observed in the gonadotropin-positive adenomas. Five of six adenomas negative for any pituitary hormones exhibited the typical papillary structure. Thus, approximately 80% of clinically non-functioning adenomas constituted a single tumor group that shared the common histologic features of gonadotroph adenomas. These findings suggest that nearly all tumor types of clinically non-functioning adenomas can be diagnosed solely by light microscopy in combination with immunohistochemistry, and that the vast majority of them may be gonadotroph adenomas.     

MicroRNAs-based network: a novel therapeutic agent in pituitary adenoma

Pituitary adenomas are common benign intracranial neoplasms representing about 10-25% of all intracranial neoplasm. Significant morbidity can occur along with pituitary adenomas due to hormonal dysfunction and mass effects. The pathogenesis of pituitary adenoma is unclear, however, etiologic factors include genetic events, hormonal stimulation, and growth factors [1], all of which promote cell proliferation and transformation in the tumor. However, genetic events play the most important role in tumorigenesis. MicroRNAs (miRNAs), a class of non-coding RNAs, not only have function in pituitary cell proliferation and apoptosis but also in neoplastic transformation. It has been shown that miRNAs are differentially expressed in pituitary adenoma when compared with the normal pituitary gland; moreover, miRNAs have been identified as a predictive signature of pituitary adenoma and can be used to predict the histotype. The expression of miRNAs can be used not only to differentiate microadenomas from macroadenomas, but to also distinguish samples of treated patients from samples of non-treated patients. Therefore, we hypothesized that a miRNA-based network may be involved in pituitary tumorigenesis and it can potentially serve as useful diagnostic markers to improve the classification of pituitary adenomas. Here, we reviewed the therapeutic potential that different types of miRNAs may play in tumorigenesis. Moreover, miRNAs may emerge as potential therapeutic targets. We speculated the mechanism of miR-21 is involved in tumorigenesis, leading to improvements in therapies and prevention of metastasis.     

Pathobiologic study of pituitary tumors: report of 62 cases with a review of the recent literature

Advances in radioimmunoassay procedures, immunocytochemistry, neuroradiologic imaging, and the surgical and medical treatment of pituitary adenomas have led to reappraisal of their classification as well as refinements in the diagnostic approaches used by pathologists. Sixty-two pituitary adenomas are described, and recent advances in this field are reviewed. Most of the patients were adults, but one of the adrenocorticotropic hormone (ACTH)-producing adenomas occurred in an 11-month-old infant. Endocrine-inactive tumors (43.5 per cent) were less common than hormone-producing tumors (56.5 per cent). Local invasion was most common in the former group, followed by ACTH-producing and other hormone-producing tumors. Ultrastructural features correlated with hormonal levels in the growth hormone(GH)-secreting tumors but not in the prolactin(LTH)- or ACTH-producing tumors. The formation of 7-nm filaments in the cytoplasm of tumor cells, corresponding to Crooke's hyaline change on light microscopy, was characteristic of ACTH-producing tumors. Ultrastructural changes in the ACTH granules suggested that the filaments may be derived from the feedback action of cortisol. Prior to surgery, a Rathke's cleft cyst and a chordoma were mistaken for endocrine-inactive pituitary adenomas. In two additional cases ectopic ACTH-producing tumors of lung clinically mimicked pituitary adenoma. Conversely, one pituitary adenoma mimicked sphenoid wing meningioma. Clinical, hormonal, and radiologic data and immunocytochemical and electron microscopic studies are needed for accurate pathologic interpretation and classification of pituitary adenomas.     

Clusterin Expression in Non-neoplastic Adenohypophyses and Pituitary Adenomas: Cytoplasmic Clusterin Localization in Adenohypophysis is Related to Aging

Clusterin is a circulating multifunctional glycoprotein produced in several kinds of epithelial and neuronal cells. Clusterin is upregulated during different physiological and pathological states, such as senescence, type-2 diabetes mellitus, Alzheimer disease, and in various neoplasms. Herein, we investigated the immunohistochemical expression of clusterin in non-neoplastic adenohypophysis of human autopsy subjects and pituitary adenomas. We also investigated the association of clusterin increase with age in adenohypophysis of autopsy subjects. Immunohistochemically, clusterin was found positive in the cytoplasm of all adenoma cases, and in the cytoplasm of parenchymal cells, stellate cells, mixed cell follicles and in colloidal material inside of the follicles of non-neoplastic adenohypophysis as well. Clusterin expression in pituitary adenomas was found significantly higher than in non-neoplastic adenohypophyses. In addition, in non-neoplastic adenohypophysis, a significant increase in clusterin expression levels between young (≤30 years), middle aged (31 to 60 years), and older (≥61 years) subjects (p < 0.00001, analysis of variance [ANOVA]) was found. In addition to clusterin accumulation, presence of calcification (p < 0.045, ANOVA) and presence of large follicles with colloid accumulation (p < 0.004, ANOVA) were also statistically significant factors related to aging in non-neoplastic adenohypophysis. In conclusion, the present study demonstrated that clusterin expression was found in non-neoplastic adenohypophysis and in upregulated amounts in pituitary adenomas. This study also demonstrated that in non-neoplastic adenohypophyses, increase of clusterin positive cells; histopathological findings of calcification or presence colloidal material accumulation in large follicles were associated with age. To our knowledge, immunohistochemical localization of clusterin in pituitary adenomas was not reported previously.     

Oncocytomas and null cell adenomas of the human pituitary: Morphometric and in vitro functional comparison

Summary In this study, light microscopic and ultrastructural morphometric features of oncocytomas and null cell adenomas were compared and the morphometric data were correlated with in vitro endocrine activity. All tumours were unassociated with clinical or biochemical evidence of hormone excess and were diagnosed as oncocytomas or null cell adenomas, using histology, immunohistochemistry and electron microscopy. In oncocytomas, when compared with null cell adenomas, light microscopic morphometry revealed that total cell areas were significantly larger and nuclear cytoplasmic ratios were smaller due to an increase in cytoplasmic areas. Ultrastructural morphometry disclosed an abundance of mitochondria in oncocytomas. Absolute volumes of cytoplasmic organelles per cell were not reduced in oncocytomas compared with those of null cell adenomas. These results indicate that accumulating mitochondria do not replace other cytoplasmic organelles, and furthermore that the functional potential of oncocytomas is not lost. In vitro study demonstrated the production of pituitary hormones, primarily gonadotropins in oncocytomas and null cell adenomas. It can be concluded that oncocytomas, which represent the final stage of oncocytic transformation, have a close relationship with null cell adenomas based on morphometric comparison as well as in vitro studies.     

Increased expression of HMGA1 correlates with tumour invasiveness and proliferation in human pituitary adenomas

Wang E L, Qian Z R, Rahman M M, Yoshimoto K, Yamada S, Kudo E & Sano T
(2010) Histopathology 56, 501–509 Increased expression of HMGA1 correlates with tumour invasiveness and proliferation in human pituitary adenomas Aims: High‐mobility group A1 (HMGA1) is highly expressed in various benign and malignant tumours. The development of pituitary adenoma in Hmga1 transgenic mice has been reported. However, no studies have investigated HMGA1 expression and its clinical significance in human pituitary adenomas. Methods and results: Immunohistochemical expression of HMGA1 was analysed with respect to various clinicopathological factors in 95 pituitary adenomas. Nuclear expression of HMGA1 was observed in 62% of pituitary adenomas, whereas normal adenohypophysial tissues were negative. Although HMGA1 expression was frequently detected in clinically non‐functioning adenomas – 90% of silent adrenocorticotropic hormone (ACTH), 76.2% of follicle‐stimulating hormone/luteinizing hormone and 100% of null cell adenomas – it was also detected in 48.1% of growth hormone (GH), 60% of mixed GH/prolactin (PRL), 62.5% of PRL, 66.6% of thyroid‐stimulating hormone and 37.5% of ACTH adenomas. HMGA1 expression was significantly higher in invasive adenomas or macroadenomas than in non‐invasive adenomas or microadenomas (invasive versus non‐invasive, P < 0.05; macroadenoma versus microadenoma, P < 0.05). In addition, HMGA1 showed the highest level in grade IV, more aggressive pituitary adenomas, than in grades I, II and III (IV versus I, P = 0.01; IV versus II, P = 0.01; IV versus III, P = 0.07). Furthermore, a significant correlation between HMGA1 expression and MIB‐1 labelling index was observed (R = 0.368, P < 0.0002). Conclusions: These findings suggest that HMGA1 up‐regulation has an important oncogenic role in pituitary tumorigenesis, as well as being a novel molecular marker of tumour proliferation and invasiveness.