Immunoreactive luteinizing hormone in functioning corticotroph adenomas of the pituitary. Immunohistochemical and tissue culture studies of two cases

Anatomy of a viral entry platform differentially functionalized by integrins α3 and α6

During cell invasion, human papillomaviruses use large CD151 patches on the cell surface. Here, we studied whether these patches are defined architectures with features for virus binding and/or internalization. Super-resolution microscopy reveals that the patches are assemblies of closely associated nanoclusters of CD151, integrin α3 and integrin α6. Integrin α6 is required for virus attachment and integrin α3 for endocytosis. We propose that CD151 organizes viral entry platforms with different types of integrin clusters for different functionalities. Since numerous viruses use tetraspanin patches, we speculate that this building principle is a blueprint for cell-surface architectures utilized by viral particles.

The 2017 World Health Organization classification of tumors of the pituitary gland: a summary

The 4th edition of the World Health Organization (WHO) classification of endocrine tumors has been recently released. In this new edition, major changes are recommended in several areas of the classification of tumors of the anterior pituitary gland (adenophypophysis). The scope of the present manuscript is to summarize these recommended changes, emphasizing a few significant topics. These changes include the following: (1) a novel approach for classifying pituitary neuroendocrine tumors according to pituitary adenohypophyseal cell lineages; (2) changes to the histological grading of pituitary neuroendocrine tumors with the elimination of the term "atypical adenoma;" and (3) introduction of new entities like the pituitary blastoma and re-definition of old entities like the null-cell adenoma. This new classification is very practical and mostly based on immunohistochemistry for pituitary hormones, pituitary-specific transcription factors, and other immunohistochemical markers commonly used in pathology practice, not requiring routine ultrastructural analysis of the tumors. Evaluation of tumor proliferation potential, by mitotic count and Ki-67 labeling index, and tumor invasion is strongly recommended on individual case basis to identify clinically aggressive adenomas. In addition, the classification offers the treating clinical team information on tumor prognosis by identifying specific variants of adenomas associated with an elevated risk for recurrence. Changes in the classification of non-neuroendocrine tumors are also proposed, in particular those tumors arising in the posterior pituitary including pituicytoma, granular cell tumor of the posterior pituitary, and spindle cell oncocytoma. These changes endorse those previously published in the 2016 WHO classification of CNS tumors. Other tumors arising in the sellar region are also reviewed in detail including craniopharyngiomas, mesenchymal and stromal tumors, germ cell tumors, and hematopoietic tumors. It is hoped that the 2017 WHO classification of pituitary tumors will establish more biologically and clinically uniform groups of tumors, make it possible for practicing pathologists to better diagnose these tumors, and contribute to our understanding of clinical outcomes for patients harboring pituitary tumors.

Silent corticogonadotroph adenomas: clinical and cellular characteristics and long-term outcomes

Silent corticotrophins adenomas (SCAs) are clinically silent and non-secreting but immunostain positively for ACTH. We hypothesize that SCAs comprise both corticotroph and gonadotroph characteristics. Cohort analysis from 1994-2008 with follow-up time ranging from 1-15 years in a tertiary referral center. We compared preoperative and postoperative clinical results and tumor cytogenesis in 25 SCAs and 84 nonfunctioning adenomas in 109 consecutive patients diagnosed pre-operatively with nonfunctioning pituitary adenomas. Clinical outcomes were radiologic and hormonal measures. Pathologic outcomes were expression of relevant pituitary hormones, tissue-specific transcription factors, and electron microscopy features. Preoperative SCA presentation was similar to that observed for nonfunctioning adenomas. However, SCAs recurred postoperatively at a median of 3 years vs. 8 years for nonfunctioning adenomas (p<0.0001). Fifty-four percent of patients with SCAs had new onset postoperative hypopituitarism vs. 17% of nonfunctioning adenomas (p<0.025). SCAs (n=18) were immunopositive for ACTH, cytoplasmic and nuclear SF-1, NeuroD1, DAX-1, and alpha-gonadotropin subunit, but Tpit negative, and co-expression of tumor ACTH with either SF-1 or LH was detected. In contrast, functional corticotroph adenomas (n=11) were immunopositive for ACTH, nuclear SF-1, NeuroD1, and Tpit, but negative for DAX-1, a gonadotroph cell transcription factor. Gonadotroph adenomas (n=23) were immunonegative for ACTH and Tpit but positive for nuclear SF-1, NeuroD1, and DAX-1. SCA electron microscopy demonstrated ultrastructural features consistent with corticotroph and gonadotroph cells. As SCAs exhibit features consistent with both corticotroph and gonadotroph cytologic origin, we propose a pathologic and clinically distinct classification of SCAs as silent corticogonadotroph adenomas.

ACTH and alpha-subunit are co-expressed in rare human pituitary corticotroph cell adenomas proposed to originate from ACTH-committed early pituitary progenitor cells

The functional differentiation of pituitary cells and adenomas follows the combination of transcription factors and co-factors in three cell lineages [growth hormone-prolactin-thyroid-stimulating hormone lineage, adrenocorticotrophic hormone (ACTH)/pro-opiomelanocortin (POMC) lineage, and follicular stimulating hormone (FSH)/luteinizing hormone (LH) lineage], which include Pit-1, GATA-2, SF-1, NeuroD1/beta2, Tpit, ERalpha, and others. Only rarely are hormones from different lineages co-expressed in the same adenoma cells. Most corticotroph cell adenomas belonging to the ACTH/POMC lineage are mono-hormonal. In our study of 89 corticotroph cell adenomas, 5 cases expressed both ACTH and alpha-subunit; these adenomas did not express any other anterior pituitary hormones or subunits. To clarify the mechanism involved, we studied the transcription factors that regulate pituitary cell differentiation. NeuroD1 and T-pit, markers of the ACTH/POMC lineage, and SF-1 and DAX-1, related to the LH/FSH cell lineage were expressed in all cases. GATA2, a synergistic factor in the gonadotroph cell lineage with SF-1, was also expressed in three of five cases. As ACTH and alpha-subunit are the earliest hormones to appear during development, we speculate that these particular adenomas are derived from committed ACTH progenitor cells. The molecular process governing functional differentiation of these adenomas requires further investigation.

Molecular determinants of pituitary cytodifferentiation

The pituitary is a complex gland and is composed of several cell types, each responsible for the production of specific hormones. In the past, it was thought that one cell could make only one hormone; the concept of plurihormonality was poorly understood. Plurihormonal adenomas were thought to be either composed of multiple cell types, each producing one hormone (plurimorphous adenomas) or composed of poorly differentiated cells that exhibited abnormal production of multiple hormones. However, the molecular factors that determine hormone production have now been identified as transcription factors that target specific hormone genes. These factors have clarified three main pathways of cell differentiation. ACTH-producing corticotrophs are determined by corticotropin upstream transcription-binding element (CUTE) proteins including neuroD1/beta 2. Bihormonal gonadotrophs require expression of steroidgenic factor (SF)-1. The complex family of Pit-1 expressing cells can mature into somatotrophs, mammosomatotrophs, lactotrophs or thyrotrophs with the additional expression of estrogen receptor (ER) alpha, which enhances PRL secretion, or thyrotroph embryonic factor (TEF) which stimulates TSH-beta production. The recognition of these molecular determinants of adenohypophysial cytodifferentiation has clarified the patterns of plurihormonality which have been recognized in pituitary adenomas and provide a framework for classification of these tumors.

The pathology of pituitary tumors

The pathologist plays an important role in the distinction of pituitary adenomas from other tumors and tumor-like lesions of the sellar region, and in the accurate morphologic characterization of pitutiary adenomas. A clinicopathologic classification of pituitary adenomas is based on cell differentiation correlated with clinical evidence of hormone secretion; this classification emphasizes clinically relevant features that can offer guidance for patient management. The application of a rational approach to the immunohistochemical analysis of these lesions can be used to evaluate pathogenetic and prognostic markers and to predict responses to specific therapeutic modalities.

The multihormonal character of pituitary adenomas: immuno-electron microscopic studies

This study investigates the multihormonal character of pituitary adenomas at the ultrastructural level. The growth hormone (GH)- and prolactin (PRL)-secreting adenomas under study consisted of many moderately or densely granulated cells and a few sparsely or slightly granulated cells. The GH-secreting adenomas showed well-developed cytoplasmic organelles and many large (250 nm or more) or medium-sized (200 nm) secretory granules, as well as a few small (70-150 nm) secretory granules. The PRL-secreting hormones exhibited poorly or slightly developed cyto-plasmic organelles and several small secretory granules. Morphologically and antigenically, these sparsely or slightly granulated cells were similar to those of clinically non-functioning (CN-F) adenomas, which appeared identical to cells expressing little or slight immunoreaction to pituitary hormones at the light microscopic level. As well as those of CN-F adenomas, the small secretory granules of both densely and sparsely granulated cells expressed little or only slight antigenicity of various hormones. Con-comitantly showing slight or moderate antigenicity of hormones biochemically unrelated to GH or PRL, the medium-sized or large secretory granules larger than 140 or 160 nm significantly exhibited intense PRL or GH antigenicity, respectively (Fisher's exact test; P < 0.05 or 0.01). Their GH or PRL antigenicity increased as they grew larger. Showing intermediate cells between sparsely and densely granulated cells, two CN-F adenomas, however, appeared to develop into growth hormone-secreting adenomas. This study led us to conclude that pituitary adenomas may originate from sparsely granulated cells with slight biochemically unrelated hormones, and that their hormonality may be selectively activated singly or multiply in the course of their development.

A composite somatotroph-corticotroph pituitary adenoma

A 76-year-old woman presented with enlargement and weakness of her hands and feet coarsening of facial features, proximal muscle weakness, and worsening of her noninsulindependent diabetes mellitus. Serum growth hormone, somatomedin-C, and prolactin levels were elevated. Thyroid function test results and serum cortisol and adrenocorticotropic hormone levels were within normal limits. Luteinizing and follicle-stimulating hormone levels were both low, suggesting possible partial hypopituitarism. Magnetic resonance imaging of the sella demonstrated a pituitary lesion that measured 2.2 x 1 x 0.5 cm; it partially obliterated the suprasellar cistern and it distorted the optic chiasm. Light microscopic and ultrastructural examination of the trans-sphenoidally resected tissues identified characteristic features of 2 discrete pituitary adenomas that were in close apposition, but they were sharply demarcated. The 2 components were a corticotroph adenoma and a sparsely granulated somatotroph adenoma. Multiple adenomas of the pituitary are not rare; however, the majority are endocrinologically "nonfunctional." We report a patient with clinical features of acromegaly whose tumor was a composite lesion: one area exhibited morphological characteristics of a corticotroph adenoma and another distinct area exhibited features of a somatotroph adenoma. The possible histogenesis is discussed.

Immunohistological studies for gastrointestinal and other hormones in acth-secreting adenomas

Eighty-nine ACTH-secreting pituitary adenomas from patients with Cushing's disease or Nelson's syndrome were investigated by immunohistochemical methods for their content of gastrin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP), bombesin, substance P, and ubiquitin as a marker for intercellular fibrils and hyalin and D11 as a marker for adrenocortical tissue. In contrast to in vitro studies reported in the relevant literature, we did not find significantly positive percentages (more than 10% of adenoma cells) for gastrin and CCK. VIP and bombesin were demonstrated in one adenoma. Among the adenomas examined, ubiquitin was found in 15% and D11 in 75%. ACTH was present in 99%, pro-γ-MSH in 21 %, β-endorphin in 13%, enkephalin in 4%, and α-subunit in 11.5%. The significance of the findings is discussed.

Silent corticotroph adenoma with multiple cysts: Pars intermedia tumor?

A silent corticotroph adenoma with multiple cysts was found incidentally at autopsy. By immunohistochemistry, most of the adenoma cells contained reactivity for adrenocorticotropic hormone and beta-endorphin; a few cells stained for beta-subunit of luteinizing hormone. The cysts, interspersed within the tumor, were lined by cuboidal epithelium with foci of stratified squamous epithelium. The lining cells contained immunoreactive keratin; some cells were positive for S-100 protein or glial fibrillary acidic protein, and a few cells were also immuno-stained for adrenocorticotropic hormone and beta-endorphin. It is suggested that this tumor may represent a neoplasm of pars intermedia derivation.

Utilization of electron microscopic techniques in the in vitro study of adenohypophysial function and regulation

Morphologic studies of human adenohypophysial cells using immunocytochemistry and electron microscopy have characterized the hormone-producing cell types of the normal gland and pituitary adenomas. The classifications which have emerged allow more accurate clinicopathologic correlations than ever before, but have also raised new questions concerning cytogenesis, pathogenesis, and structure-function correlations. We report the results of studies which marry the conventional morphologic techniques of light microscopy, immunohistochemistry, electron microscopy, and ultrastructural immunocytology with functional analyses using tissue culture and radioimmunoassay of hormones released into culture media. The hormone secretory activity of nontumorous and adenomatous pituitary cells is correlated with their structural features; their secretory responses to several adenohypophysiotropic factors are compared with morphologic alterations which are characterized at the light and electron microscopic levels by morphometric analysis. These studies have shown that hypothalamic stimulating hormones increase hormone release by their target cells and alter the ultrastructural appearance of the affected cells by increasing organelles involved in hormone synthesis. Inhibitory drugs and adrenal and gonadal steroids are capable of suppressing hormone release by some tumors and also give rise to morphologic changes which correlate with the functional inhibition. Hormone release by clinically nonfunctioning adenomas has been characterized and the behavior of these tumor cells in vitro sheds some light on the reasons for lack of clinical symptomatology. The plurihormonal nature of several nontumorous and adenomatous pituitary cell types has been characterized in vitro. The results of these studies provide the basis for more accurate structure-function correlations which can be used to study the hormonal milieu in vivo, to predict the role of pathogenetic factors in pituitary tumorigenesis, and to assess the therapeutic value of stimulating or inhibiting hormones and drugs.

Changes in hormone production of a recurrent silent corticotroph adenoma of the pituitary: a histologic, immunohistochemical, ultrastructural, and tissue culture study

A 19-year-old man with blurred vision, headache, and no signs or symptoms of hormone excess was found to have a pituitary adenoma. The tumor was removed by a transfrontal approach. He had postoperative radiation therapy, but subsequently had three recurrences, all removed surgically. By histology, the tumor was a chromophobic, slightly acidophilic pituitary adenoma. Immunohistochemistry revealed the presence of adrenocorticotropin (ACTH) in all four biopsies, alpha-subunit of glycoprotein hormones, and, to a lesser extent, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the third and fourth tumor resection specimens. Ultrastructurally, the tumor had typical features of a silent corticotroph adenoma subtype 2. In tissue culture, the second, third, and fourth specimens released ACTH, alpha-subunit, FSH, and LH and responded to corticotropin-releasing hormone with increased release of ACTH, alpha-subunit, FSH, and LH. To our knowledge only one silent corticotroph adenoma has been reported previously which expressed plurihormonality. Change in immunohistochemical profile in malignant tumors is a well-known phenomenon; however, it was not reported previously in benign pituitary adenomas. The factors accounting for changing tumor phenotype are unknown.