Structure, Function, and Morphology in the Classification of Pituitary Neuroendocrine Tumors: the Importance of Routine Analysis of Pituitary Transcription Factors

Double PitNETs: A Case Report and Literature Review

Double pituitary neuroendocrine tumors (double PitNETs) are two distinct tumors in the same gland and are infrequent in clinical practice. In typical double PitNETs, an MRI detects two separate tumors that are diagnosed by pathology; they could also appear as a single tumor, and pathology would then identify the two independent tumors. A literature review was conducted, and 142 cases were analyzed to determine the characteristics of double PitNETs. Of these cases, acromegaly (45.5%) was the most common clinical feature, followed by Cushing's disease (35.1%) and prolactinoma (17.9%), indicating that double PitNETs are usually noticed by hormonal excess symptoms due to at least one functional tumor. The pathological analysis of 284 tumors showed that somatotroph (28.9%) and corticotroph (26.8%) tumors were predominant, with a recent increase in the proportion of gonadotroph tumors. Regarding transcription factors, 51.1% were of GH-PRL-TSH PIT1-lineage, 26.1% ACTH TPIT-lineage, and 17.9% LH-FSH SF1-lineage. The radiological analysis of 82 cases revealed that double tumors (45.1%) and single tumors (47.6%) were comparable, suggesting that double PitNETs are often detected as a single tumor, and attention should be paid to hidden micro-tumors during surgery. Double PitNETs are complicated by a wide variety of clinical, radiological, and pathological findings, but diagnostic and therapeutic approaches are advancing.

Multilineage Pituitary Neuroendocrine Tumors Expressing TPIT and SF1: A Clinicopathological Series of Six Tumors

Tumors of adenohypophysial hormone-secreting cells, now classified as pituitary neuroendocrine tumors (PitNETs), have been subclassified based on cell differentiation. Normal adenohypophysial cells have three lineages of differentiation driven by the transcription factors PIT1, TPIT, and SF1 which are responsible for the regulation of hormone gene expression; PIT1 drives expression of GH, PRL, and TSH, TPIT is required for POMC expression that gives rise to ACTH, and SF1 is the transcription factor responsible for FSH and LH expression. The vast majority of PitNETs follow these three lineage differentiation pathways but rare PitNETs show either no lineage differentiation or express biomarkers of more than one lineage. The recent WHO classification continued the terminology "plurihormonal" for tumors that have features of more than one lineage but a better term is "multilineage" since some tumors may express more than one lineage-specific transcription factor without the hormones that are driven by those factors. Recent data indicate that tumors with expression of PIT1 and SF1 are the most common multilineage PitNETs. Here we report the existence of rare PitNETs that express TPIT and SF1. The 6 patients (5 female, 1 male; mean age 54.8 years; range 35-84 years) represent less than 1% of patients in our series of PitNETs. Most patients had clinically silent tumors with no evidence of hormone excess and variable degrees of hypopituitarism; two had Cushing disease. All patients had macrotumors with a mean tumor size of 2.46 cm (range 1.1-5.0 cm). Crooke's hyaline change was identified in the nontumorous adenohypophysis of the two patients with Cushing disease. The mean Ki67 labeling index was 2.91% (range 2.03-3.94%). All tumors were negative for PIT1 and PIT1-lineage hormones (GH, PRL, and TSH). TPIT was focal in one tumor, and the remaining tumors had diffuse reactivity in more than 50% of tumor cells. SF1 expression was focal in 5 tumors and diffuse in one. Three tumors had variable expression of at least one gonadotropin (FSH or LH). GATA3 was expressed in two tumors. Variable ER-alpha expression was noted in three tumors. CAM5.2 was positive in all tumors. With the exception of two tumors causing Cushing disease, p27 expression was intact. Our study confirms that multilineage PitNETs expressing TPIT and SF1 occur but are extremely rare; they can be clinically non-functional or can cause Cushing disease. Irrespective of functional status of a PitNET, routine application of pituitary transcription factors is warranted to identify these tumors. Data on the molecular correlates and clinical significance are still needed for these rare multilineage PitNETs.

Granulation Patterns of Functional Corticotroph Tumors Correlate with Tumor Size, Proliferative Activity, T2 Intensity-to-White Matter Ratio, and Postsurgical Early Biochemical Remission

Unlike somatotroph tumors, the data on correlates of tumor granulation patterns in functional TPIT lineage pituitary neuroendocrine tumors (corticotroph tumors) have been less uniformly documented in most clinical series. This study evaluated characteristics of 41 well-characterized functional corticotroph tumors consisting of 28 densely granulated corticotroph tumors (DGCTs) and 13 sparsely granulated corticotroph tumors (SGCTs) with respect to preoperative clinical and radiological findings, tumor proliferative activity (including mitotic count and Ki-67 labeling index), and postoperative early biochemical remission rates. The median (interquartile range (IQR)) tumor size was significantly larger in the SGCT group [16.00 (16.00) mm in SGCT vs 8.5 (9.75) mm in DGCT, p = 0.049]. T2-weighted signal intensity and T2 intensity (quantitative) did not yield statistical significance based on tumor granulation; however, the T2 intensity-to-white matter ratio was significantly higher in SGCTs (p = 0.049). The median (IQR) Ki-67 labeling index was 2.00% (IQR 1.00%) in the DGCT group and 4.00% (IQR 7.00%) in the SGCT group (p = 0.043). The mitotic count per 2 mm2 was higher in the SGCT group (p = 0.001). In the multivariate analysis, the sparse granulation pattern (SGCT) remained an independent predictor of a lower probability of early biochemical remission irrespective of the tumor size and proliferative activity (p = 0.012). The current study further supports the impact of tumor granulation pattern as a biologic variable and warrants the detailed histological subtyping of functional corticotroph tumors as indicated in the WHO classification of pituitary neuroendocrine tumors. More importantly, the assessment of the quantitative T2 intensity-to-white matter ratio may serve as a preoperative radiological harbinger of SGCTs.

Plurihormonal Pituitary Neuroendocrine Tumours - A Single Centre Experience

Introduction. Plurihormonal pituitary neuroendocrine tumours (PitNET)/adenomas are pituitary neuroendocrine tumours composed of monomorphous cell populations expressing anterior pituitary transcription factors and/or hormones belonging to more than one cell lineage. Studies dedicated to plurihormonal tumours are rare and quite heterogenous with their results, bearing in mind changes in diagnostic criteria and inconsistent use of antibodies for anterior pituitary transcription factors in the diagnostic immunohistochemical panel. Material and Methods. We retrospectively analysed all patients surgically treated for PitNETs from 2016 to July 2022 in a tertiary healthcare institution. All tumours previously diagnosed PitNETs with the word "plurihormonal" were re-examined and potentially re-classified, according to 2022 WHO classification of endocrine tumours. Results. Among 721 patients surgically treated for PitNET in 5.5 years period, the diagnosis of plurihormonal PitNET was established in 11 tumours (1.3%). All tumours showed diffuse and intensive positivity for anterior pituitary transcription factors PIT1 and SF1. Clinically, all patients presented with acromegaly. Conclusions. Retrospective studies related to newly defined plurihormonal PitNETs with a reassessment of diagnoses are necessary due to their rarity and ambition to investigate their origin and biological behaviour. The fact that the majority of plurihormonal PitNETs are clinically presented with acromegaly and show simultaneous positivity to PIT1 and SF1 transcription factors deserve special attention and need for further research in larger cohorts of these exceptional tumours.

Transcription Factor Immunohistochemistry in the Classification of Pituitary Neuroendocrine Tumor/Adenoma: Proposal in a Limited-Resource Setting

CONTEXT.—

Pituitary neuroendocrine tumors/adenomas are common intracranial tumors that require accurate subtyping because each tumor differs in its biologic behavior and response to treatment. Pituitary-specific transcription factors allow for improved lineage identification and diagnosis of newly introduced variants.

OBJECTIVE.—

To assess the usefulness of transcription factors and design a limited panel of immunostains for classification of pituitary neuroendocrine tumors/adenoma.

DESIGN.—

A total of 356 tumors were classified as per expression of pituitary hormones and transcription factors T-box family member TBX19 (TPIT), pituitary-specific POU-class homeodomain (PIT1), and steroidogenic factor-1 (SF-1). The resultant classification was correlated with patients' clinical and biochemical features. The performance and relevance of individual immunostains were analyzed.

RESULTS.—

Reclassification of 34.8% (124 of 356) of pituitary neuroendocrine tumors/adenoma was done after application of transcription factors. The highest agreement with final diagnosis was seen using a combination of hormone and transcription factors. SF-1 had higher sensitivity, specificity, and predictive value compared with follicle-stimulating hormone and luteinizing hormone. On the other hand, TPIT and PIT1 had similar performance and Allred scores compared with their respective hormones.

CONCLUSIONS.—

SF-1 and PIT1 should be included in the routine panel for guiding the classification. PIT1 positivity needs to be followed by hormone immunohistochemistry, especially in nonfunctional cases. TPIT and adrenocorticotropin can be used interchangeably as per availability of the lab.

Plurihormonal Pituitary Neuroendocrine Tumors: Clinical Relevance of Immunohistochemical Analysis

Plurihormonal pituitary neuroendocrine tumors (PitNETs) are rare forms of tumors that express more than one hormone. The most common association is between growth hormone (GH) and prolactin (PRL), but other unusual combinations have been reported, such as GH and ACTH. Usually, the clinical dominance in these cases is related to GH hypersecretion. In these cases, immunohistochemistry (IHC) of transcription factors (TFs) is very useful for an accurate diagnosis. We included 42 patients diagnosed with pituitary neuroendocrine tumors (PitNETs): 37 patients with a confirmed diagnosis of acromegaly, and 5 patients with prolactinomas. All patients underwent transsphenoidal surgical intervention. We correlated the immunohistochemical features of plurihormonal PitNETs with clinical, hormonal, and imaging data. Tumor specimens were histologically and immunohistochemically examined. Based on the 2022 WHO classification, using IHC, 13 patients exhibited positive staining for more than one hormone, while unusual combinations like GH + ACTH and PRL + ACTH were also identified in other cases. Unusual cell combinations that produce hormones unrelated histogenetically, biochemically, or through regulatory mechanisms can appear and may display aggressive behavior, persistent disease, and high recurrence. We have not identified a clear correlation with the prognosis of these rare PitNETs.

[Unification of pathomorphological examination of patients with neuroendocrine tumors of the pituitary gland. Controversial issues of the new classification]

The progressive improvement of the classification using modern analytical methods is an essential tool for the development of precise and personalized approaches to the treatment of pituitary adenomas. In recent years, endocrinologists have witnessed evolutionary changes that have occurred in the histopathological identification of pituitary neoplasms, revealing new possibilities for studying tumorigenesis and predicting biological behavior.The paper considers the historical aspects of the gradual improvement of the classification of pituitary adenomas, as well as the new international 2022 WHO classification, according to which pituitary adenomas are included in the list of neuroendocrine tumors (PitNETs) to reflect the biological aggressiveness of some non-metastatic pituitary adenomas. The characteristics of pituitary adenoma are presented, as well as a list of histological subtypes of aggressive neuroendocrine tumors of the pituitary gland, marked by the main potentials for invasive growth, an increased risk of recurrence and a negative clinical prognosis.The expediency of changing the definition of «pituitary adenoma» to «neuroendocrine tumor» is discussed. It is emphasized that the introduction of a unified clinical, laboratory and morphological protocol into national clinical practice will help provide comparable comparative studies on the prognosis of the disease and the effectiveness of secondary therapy and also contribute to adequate management of potentially aggressive PitNETs.

Top 10 Histological Mimics of Neuroendocrine Carcinoma You Should Not Miss in the Head and Neck

BACKGROUND

The spectrum of neuroendocrine neoplasia (NEN) of the head and neck region is wide-ranging and diverse, including a variety of diagnoses stretching from benign and low-malignant tumor forms to highly proliferative, poor prognosis neuroendocrine carcinoma (NEC). Moreover, there are several non-neuroendocrine differential diagnoses to keep in mind as well, displaying various degree of morphological and/or immunohistochemical overlap with bona fide neuroendocrine lesions.

METHODS

Review.

RESULTS

While the growth patterns may vary, well-differentiated NEN usually display a stippled "salt and pepper" chromatin, a granular cytoplasm, and unequivocal expression of neuroendocrine markers such as chromogranin A and synaptophysin. However, these features are often less pronounced in NEC, which may cause diagnostic confusion-not the least since several non-NEC head and neck tumors may exhibit morphological similarities and focal neuroendocrine differentiation.

CONCLUSION

As patients with NEC may require specific adjuvant treatment and follow-up, knowledge regarding differential diagnoses and potential pitfalls is therefore clinically relevant. In this review, the top ten morphological and/or immunohistochemical mimics of NEC are detailed in terms of histology, immunohistochemistry, and molecular genetics.

The Complex Histopathological and Immunohistochemical Spectrum of Neuroendocrine Tumors-An Overview of the Latest Classifications

Neuroendocrine neoplasms (NENs) originate from the neuroendocrine cell system, which may either take the shape of organoid cell aggregations or be composed of dispersed cells across various organs. Therefore, these tumors are heterogenous regarding the site of origin, functional status, degree of aggressiveness, and prognosis. When treating patients with neuroendocrine tumors, one of the most significant challenges for physicians is determining the correct tumor grade and thus classifying patients into risk categories. Over the years, the classification of these tumors has changed significantly, often causing confusion due to clinical, molecular, and immunohistochemical variability. This review aims to outline the latest NENs classifications regardless of their site of origin. Thus, an overview of the key histopathological and immunohistochemical characteristics of NENs could pave the way to validate possible predictive and prognostic markers and also guide the therapeutic conduct.

Alternative Lengthening of Telomeres (ALT) and Telomerase Reverse Transcriptase Promoter Methylation in Recurrent Adult and Primary Pediatric Pituitary Neuroendocrine Tumors

Neoplastic cells acquire the ability to proliferate endlessly by maintaining telomeres via telomerase, or alternative lengthening of telomeres (ALT). The role of telomere maintenance in pituitary neuroendocrine tumors (PitNETs) has yet to be thoroughly investigated. We analyzed surgical samples of 24 adult recurrent PitNETs (including onset and relapses for 14 of them) and 12 pediatric primary PitNETs. The presence of ALT was assessed using telomere-specific fluorescence in situ hybridization, methylation of telomerase reverse transcriptase promoter (TERTp) by methylation-specific PCR, and ATRX expression by immunohistochemistry. Among the adult recurrent PitNETs, we identified 3/24 (12.5%) ALT-positive cases. ALT was present from the onset and maintained in subsequent relapses, suggesting that this mechanism occurs early in tumorigenesis and is stable during progression. ATRX loss was only seen in one ALT-positive case. Noteworthy, ALT was observed in 3 out of 5 aggressive PitNETs, including two aggressive corticotroph tumors, eventually leading to patient's death. ALT-negative tumors (87.5%) were classified according to their low (29.2%), medium (50%), and high (8.3%) telomere fluorescence intensity, with no significant differences emerging in their molecular, clinical, or pathological characteristics. TERTp methylation was found in 6/24 cases (25%), with a total concordance in methylation status between onset and recurrences, suggesting that this mechanism remains stable throughout disease progression. TERTp methylation did not influence telomere length. In the pediatric cohort of PitNETs, TERTp methylation was also observed in 4/12 cases (33.3%), but no case of ALT activation was observed. In conclusion, ALT is triggered at onset and maintained during tumor progression in a subset of adult PitNETs, suggesting that it could be used for clinical purposes, as a potential predictor of aggressive behavior.

Silent Corticotroph Tumor with Adrenocortical Choristoma in an Eleven-year-old Boy

Silent corticotroph tumors are composed of corticotroph cells, but do not manifest any biochemical or clinical evidence of hypercortisolism. A choristoma is a benign, congenital proliferation of histologically mature tissue elements normally not present at the site of occurrence. The existence of adrenocortical cells within the pituitary gland, which can be explained as a choristoma, is a very rare entity, and the co-occurrence of these two entities have only been reported in few cases. We report an 11-year-old boy with central hypothyroidism. On cranial magnetic resonance imaging a pituitary tumor was detected, and histopathological studies led to a diagnosis of an adrenal choristoma and a silent corticotroph tumor in the pituitary gland. The presence of adrenocortical cells were confirmed by positive calretinin, inhibin and Melan A staining, and the corticotroph cells by immunohistochemistry demonstrating adrenocorticotropic hormone positivity. Herein, we report the fourth and the youngest case of silent corticotroph tumor with adrenocortical choristoma in the literature. Even though the underlying mechanism is not fully understood, suggested mechanisms are discussed.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Overview of the 2022 WHO Classification of Head and Neck Neuroendocrine Neoplasms

This review article provides a brief overview of the new WHO classification by adopting a question-answer model to highlight the spectrum of head and neck neuroendocrine neoplasms which includes epithelial neuroendocrine neoplasms (neuroendocrine tumors and neuroendocrine carcinomas) arising from upper aerodigestive tract and salivary glands, and special neuroendocrine neoplasms including middle ear neuroendocrine tumors (MeNET), ectopic or invasive pituitary neuroendocrine tumors (PitNET; formerly known as pituitary adenoma) and Merkel cell carcinoma as well as non-epithelial neuroendocrine neoplasms (paragangliomas). The new WHO classification follows the IARC/WHO nomenclature framework and restricts the diagnostic term of neuroendocrine carcinoma to poorly differentiated epithelial neuroendocrine neoplasms. In this classification, well-differentiated epithelial neuroendocrine neoplasms are termed as neuroendocrine tumors (NET), and are graded as G1 NET (no necrosis and < 2 mitoses per 2 mm²; Ki67 < 20%), G2 NET (necrosis or 2-10 mitoses per 2 mm², and Ki67 < 20%) and G3 NET (> 10 mitoses per 2 mm² or Ki67 > 20%, and absence of poorly differentiated cytomorphology). Neuroendocrine carcinomas (> 10 mitoses per 2 mm², Ki67 > 20%, and often associated with a Ki67 > 55%) are further subtyped based on cytomorphological characteristics as small cell and large cell neuroendocrine carcinomas. Unlike neuroendocrine carcinomas, head and neck NETs typically show no aberrant p53 expression or loss of RB reactivity. Ectopic or invasive PitNETs are subtyped using pituitary transcription factors (PIT1, TPIT, SF1, GATA3, ER-alpha), hormones and keratins (e.g., CAM5.2). The new classification emphasizes a strict correlation of morphology and immunohistochemical findings in the accurate diagnosis of neuroendocrine neoplasms. A particular emphasis on the role of biomarkers in the confirmation of the neuroendocrine nature of a neoplasm and in the distinction of various neuroendocrine neoplasms is provided by reviewing ancillary tools that are available to pathologists in the diagnostic workup of head and neck neuroendocrine neoplasms. Furthermore, the role of molecular immunohistochemistry in the diagnostic workup of head and neck paragangliomas is discussed. The unmet needs in the field of head and neck neuroendocrine neoplasms are also discussed in this article. The new WHO classification is an important step forward to ensure accurate diagnosis that will also form the basis of ongoing research in this field.

Overview of the 2022 WHO Classification of Paragangliomas and Pheochromocytomas

This review summarizes the classification of tumors of the adrenal medulla and extra-adrenal paraganglia as outlined in the 5th series of the WHO Classification of Endocrine and Neuroendocrine Tumors. The non-epithelial neuroendocrine neoplasms (NENs) known as paragangliomas produce predominantly catecholamines and secrete them into the bloodstream like hormones, and they represent a group of NENs that have exceptionally high genetic predisposition. This classification discusses the embryologic derivation of the cells that give rise to these lesions and the historical evolution of the terminology used to classify their tumors; paragangliomas can be sympathetic or parasympathetic and the term pheochromocytoma is used specifically for intra-adrenal paragangliomas that represent the classical sympathetic form. In addition to the general neuroendocrine cell biomarkers INSM1, synaptophysin, and chromogranins, these tumors are typically negative for keratins and instead have highly specific biomarkers, including the GATA3 transcription factor and enzymes involved in catecholamine biosynthesis: tyrosine hydroxylase that converts L-tyrosine to L-DOPA as the rate-limiting step in catecholamine biosynthesis, dopamine beta-hydroxylase that is present in cells expressing norepinephrine, and phenylethanolamine N-methyltransferase, which converts norepinephrine to epinephrine and therefore can be used to distinguish tumors that make epinephrine. In addition to these important tools that can be used to confirm the diagnosis of a paraganglioma, new tools are recommended to determine genetic predisposition syndromes; in addition to the identification of precursor lesions, molecular immunohistochemistry can serve to identify associations with SDHx, VHL, FH, MAX, and MEN1 mutations, as well as pseudohypoxia-related pathogenesis. Paragangliomas have a well-formed network of sustentacular cells that express SOX10 and S100, but this is not a distinctive feature, as other epithelial NENs also have sustentacular cells. Indeed, it is the presence of such cells and the association with ganglion cells that led to a misinterpretation of several unusual lesions as paragangliomas; in the 2022 WHO classification, the tumor formerly known as cauda equina paraganglioma is now classified as cauda equina neuroendocrine tumor and the lesion known as gangliocytic paraganglioma has been renamed composite gangliocytoma/neuroma and neuroendocrine tumor (CoGNET). Since the 4th edition of the WHO, paragangliomas have no longer been classified as benign and malignant, as any lesion can have metastatic potential and there are no clear-cut features that can predict metastatic behavior. Moreover, some tumors are lethal without metastatic spread, by nature of local invasion involving critical structures. Nevertheless, there are features that can be used to identify more aggressive lesions; the WHO does not endorse the various scoring systems that are reviewed but also does not discourage their use. The identification of metastases is also complex, particularly in patients with germline predisposition syndromes, since multiple lesions may represent multifocal primary tumors rather than metastatic spread; the identification of paragangliomas in unusual locations such as lung or liver is not diagnostic of metastasis, since these may be primary sites. The value of sustentacular cells and Ki67 labeling as prognostic features is also discussed in this new classification. A staging system for pheochromocytoma and extra-adrenal sympathetic PGLs, introduced in the 8th Edition AJCC Cancer Staging Manual, is now included. This paper also provides a summary of the criteria for the diagnosis of a composite paragangliomas and summarizes the classification of neuroblastic tumors. This review adopts a practical question-answer framework to provide members of the multidisciplinary endocrine oncology team with a most up-to-date approach to tumors of the adrenal medulla and extra-adrenal paraganglia.

Overview of the 2022 WHO Classification of Adrenal Cortical Tumors

The new WHO classification of adrenal cortical proliferations reflects translational advances in the fields of endocrine pathology, oncology and molecular biology. By adopting a question-answer framework, this review highlights advances in knowledge of histological features, ancillary studies, and associated genetic findings that increase the understanding of the adrenal cortex pathologies that are now reflected in the 2022 WHO classification. The pathological correlates of adrenal cortical proliferations include diffuse adrenal cortical hyperplasia, adrenal cortical nodular disease, adrenal cortical adenomas and adrenal cortical carcinomas. Understanding germline susceptibility and the clonal-neoplastic nature of individual adrenal cortical nodules in primary bilateral macronodular adrenal cortical disease, and recognition of the clonal-neoplastic nature of incidentally discovered non-functional subcentimeter benign adrenal cortical nodules has led to redefining the spectrum of adrenal cortical nodular disease. As a consequence, the most significant nomenclature change in the field of adrenal cortical pathology involves the refined classification of adrenal cortical nodular disease which now includes (a) sporadic nodular adrenocortical disease, (b) bilateral micronodular adrenal cortical disease, and (c) bilateral macronodular adrenal cortical disease (formerly known primary bilateral macronodular adrenal cortical hyperplasia). This group of clinicopathological entities are reflected in functional adrenal cortical pathologies. Aldosterone producing cortical lesions can be unifocal or multifocal, and may be bilateral with no imaging-detected nodule(s). Furthermore, not all grossly or radiologically identified adrenal cortical lesions may be the source of aldosterone excess. For this reason, the new WHO classification endorses the nomenclature of the HISTALDO classification which uses CYP11B2 immunohistochemistry to identify functional sites of aldosterone production to help predict the risk of bilateral disease in primary aldosteronism. Adrenal cortical carcinomas are subtyped based on their morphological features to include conventional, oncocytic, myxoid, and sarcomatoid subtypes. Although the classic histopathologic criteria for diagnosing adrenal cortical carcinomas have not changed, the 2022 WHO classification underscores the diagnostic and prognostic impact of angioinvasion (vascular invasion) in these tumors. Microscopic angioinvasion is defined as tumor cells invading through a vessel wall and forming a thrombus/fibrin-tumor complex or intravascular tumor cells admixed with platelet thrombus/fibrin. In addition to well-established Weiss and modified Weiss scoring systems, the new WHO classification also expands on the use of other multiparameter diagnostic algorithms (reticulin algorithm, Lin-Weiss-Bisceglia system, and Helsinki scoring system) to assist the workup of adrenal cortical neoplasms in adults. Accordingly, conventional carcinomas can be assessed using all multiparameter diagnostic schemes, whereas oncocytic neoplasms can be assessed using the Lin-Weiss-Bisceglia system, reticulin algorithm and Helsinki scoring system. Pediatric adrenal cortical neoplasms are assessed using the Wieneke system. Most adult adrenal cortical carcinomas show > 5 mitoses per 10 mm² and > 5% Ki67. The 2022 WHO classification places an emphasis on an accurate assessment of tumor proliferation rate using both the mitotic count (mitoses per 10 mm²) and Ki67 labeling index which play an essential role in the dynamic risk stratification of affected patients. Low grade carcinomas have mitotic rate of ≤ 20 mitoses per 10 mm², whereas high-grade carcinomas show > 20 mitoses per 10 mm². Ki67-based tumor grading has not been endorsed in the new WHO classification, since the proliferation indices are continuous variables rather than being static thresholds in tumor biology. This new WHO classification emphasizes the role of diagnostic and predictive biomarkers in the workup of adrenal cortical neoplasms. Confirmation of the adrenal cortical origin of a tumor remains a critical requirement when dealing with non-functional lesions in the adrenal gland which may be mistaken for a primary adrenal cortical neoplasm. While SF1 is the most reliable biomarker in the confirmation of adrenal cortical origin, paranuclear IGF2 expression is a useful biomarker in the distinction of malignancy in adrenal cortical neoplasms. In addition to adrenal myelolipoma, the new classification of adrenal cortical tumors has introduced new sections including adrenal ectopia, based on the potential role of such ectopic tissue as a possible source of neoplastic proliferations as well as a potential mimicker of metastatic disease. Adrenal cysts are also discussed in the new classification as they may simulate primary cystic adrenal neoplasms or even adrenal cortical carcinomas in the setting of an adrenal pseudocyst.

Overview of the 2022 WHO Classification of Neuroendocrine Neoplasms

In this review, we detail the changes and the relevant features that are applied to neuroendocrine neoplasms (NENs) in the 2022 WHO Classification of Endocrine and Neuroendocrine Tumors. Using a question-and-answer approach, we discuss the consolidation of the nomenclature that distinguishes neuronal paragangliomas from epithelial neoplasms, which are divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). The criteria for these distinctions based on differentiation are outlined. NETs are generally (but not always) graded as G1, G2, and G3 based on proliferation, whereas NECs are by definition high grade; the importance of Ki67 as a tool for classification and grading is emphasized. The clinical relevance of proper classification is explained, and the importance of hormonal function is examined, including eutopic and ectopic hormone production. The tools available to pathologists for accurate classification include the conventional biomarkers of neuroendocrine lineage and differentiation, INSM1, synaptophysin, chromogranins, and somatostatin receptors (SSTRs), but also include transcription factors that can identify the site of origin of a metastatic lesion of unknown primary site, as well as hormones, enzymes, and keratins that play a role in functional and structural correlation. The recognition of highly proliferative, well-differentiated NETs has resulted in the need for biomarkers that can distinguish these G3 NETs from NECs, including stains to determine expression of SSTRs and those that can indicate the unique molecular pathogenetic alterations that underlie the distinction, for example, global loss of RB and aberrant p53 in pancreatic NECs compared with loss of ATRX, DAXX, and menin in pancreatic NETs. Other differential diagnoses are discussed with recommendations for biomarkers that can assist in correct classification, including the distinctions between epithelial and non-epithelial NENs that have allowed reclassification of epithelial NETs in the spine, in the duodenum, and in the middle ear; the first two may be composite tumors with neuronal and glial elements, and as this feature is integral to the duodenal lesion, it is now classified as composite gangliocytoma/neuroma and neuroendocrine tumor (CoGNET). The many other aspects of differential diagnosis are detailed with recommendations for biomarkers that can distinguish NENs from non-neuroendocrine lesions that can mimic their morphology. The concepts of mixed neuroendocrine and non-neuroendocrine (MiNEN) and amphicrine tumors are clarified with information about how to approach such lesions in routine practice. Theranostic biomarkers that assist patient management are reviewed. Given the significant proportion of NENs that are associated with germline mutations that predispose to this disease, we explain the role of the pathologist in identifying precursor lesions and applying molecular immunohistochemistry to guide genetic testing.

Overview of the 2022 WHO Classification of Pituitary Tumors

This review summarizes the changes in the 5th Edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the pituitary gland. The new classification clearly distinguishes anterior lobe (adenohypophyseal) from posterior lobe (neurohypophyseal) and hypothalamic tumors. Other tumors arising in the sellar region are also discussed. Anterior lobe tumors include (i) well-differentiated adenohypophyseal tumors that are now classified as pituitary neuroendocrine tumors (PitNETs; formerly known as pituitary adenomas), (ii) pituitary blastoma, and (iii) the two types of craniopharyngioma. The new WHO classification provides detailed histological subtyping of a PitNET based on the tumor cell lineage, cell type, and related characteristics. The routine use of immunohistochemistry for pituitary transcription factors (PIT1, TPIT, SF1, GATA3, and ERα) is endorsed in this classification. The major PIT1, TPIT, and SF1 lineage-defined PitNET types and subtypes feature distinct morphologic, molecular, and clinical differences. The "null cell" tumor, which is a diagnosis of exclusion, is reserved for PitNETs with no evidence of adenohypophyseal lineage differentiation. Unlike the 2017 WHO classification, mammosomatotroph and acidophil stem cell tumors represent distinct PIT1-lineage PitNETs. The diagnostic category of PIT1-positive plurihormonal tumor that was introduced in the 2017 WHO classification is replaced by two clinicopathologically distinct PitNETs: the immature PIT1-lineage tumor (formerly known as silent subtype 3 tumor) and the mature plurihormonal PIT1-lineage tumor. Rare unusual plurihormonal tumors feature multi-lineage differentiation. The importance of recognizing multiple synchronous PitNETs is emphasized to avoid misclassification. The term "metastatic PitNET" is advocated to replace the previous terminology "pituitary carcinoma" in order to avoid confusion with neuroendocrine carcinoma (a poorly differentiated epithelial neuroendocrine neoplasm). Subtypes of PitNETs that are associated with a high risk of adverse biology are emphasized within their cell lineage and cell type as well as based on clinical variables. Posterior lobe tumors, the family of pituicyte tumors, include the traditional pituicytoma, the oncocytic form (spindle cell oncocytoma), the granular cell form (granular cell tumor), and the ependymal type (sellar ependymoma). Although these historical terms are entrenched in the literature, they are nonspecific and confusing, such that oncocytic pituicytoma, granular cell pituicytoma, and ependymal pituicytoma are now proposed as more accurate. Tumors with hypothalamic neuronal differentiation are classified as gangliocytomas or neurocytomas based on large and small cell size, respectively. This classification sets the standard for a high degree of sophistication to allow individualized patient management approaches.

Clinical Relevance of New World Health Organization Classification System for Pituitary Adenomas: A Validation Study With 2-Year Experience

Background

The new World Health Organization (WHO) classification system proposed a cell lineage-based classification scheme for pituitary adenomas in which transcription factors (TFs) play a major role as key classifiers. We aimed to evaluate clinical relevance of the new classification system in a clinical setting.

Methods

TF staining was retrospectively performed for 153 clinically and histologically well characterized pituitary adenomas. Then, 484 pituitary adenomas were prospectively stained for TFs and then for relevant pituitary hormones. TF and hormone stain-based diagnoses were compared, and differences in clinical manifestations were evaluated.

Results

The accuracies of antibodies for three TFs were successfully validated and had an overall matching rate was 89.6%. We identified 50 (10.4%) cases with discrepancies between TF and pituitary hormone stains. Gonadotroph adenomas lacking follicle-stimulating hormone and luteinizing hormone stains account for most discrepancies. Null cell adenomas may be more prevalent than reported and may be clinically more aggressive than gonadotroph adenomas.

Conclusion

The new WHO classification is mostly well matched with the traditional classification. However, until the new classification is further validated and interpreted in the context of long-term clinical outcomes, routine histological examination should include full slate of immunostains for pituitary hormones as well as TFs.

Challenges in the Diagnosis of Pituitary Neuroendocrine Tumors

Detailed analysis of cytodifferentiation and hormone production has classified pituitary neuroendocrine tumors (PitNETs) in a formal system that reflects the lineage differentiation of nontumorous adenohypophysial cells as well as subtypes of tumors that have predictive value. In addition, tumors composed of cells that lack terminal differentiation are well characterized. To comply with the proposal to create an overarching classification of neuroendocrine neoplasia, these tumors are now called PitNETs rather than adenomas. The next important step will be to relinquish the term "pituitary carcinoma" for metastatic PitNETs that remain well differentiated, and to alter the terminology used for tumors that are not terminally differentiated to reflect only their immature lineage. The existence of mixed neuroendocrine and non-neuroendocrine neoplasms (MiNENs) similar to those at other body sites is proven by mixed craniopharyngiomas with PitNETs. As with other NETs, these neoplasms should be reported with synoptic data that guide completeness of reporting. A formal system of grading should be created, but not only based on proliferation, as these tumors have shown the prognostic value of cytodifferentiation. A formal system of staging should also be devised to complement grade in the thorough and accurate diagnosis of tumors that arise from adenohypophysial cells.

Epithelial-Mesenchymal Transition in the Resistance to Somatostatin Receptor Ligands in Acromegaly

Epithelial-mesenchymal transition (EMT) is a dynamic process by which epithelial cells loss their phenotype and acquire mesenchymal traits, including increased migratory and invasive capacities. EMT is involved in physiological processes, such as embryogenesis and wound healing, and in pathological processes such as cancer, playing a pivotal role in tumor progression and metastasis. Pituitary tumors, although typically benign, can be locally invasive. Different studies have shown the association of EMT with increased tumor size and invasion in pituitary tumors, and in particular with a poor response to Somatostatin Receptor Ligands (SRLs) treatment in GH-producing pituitary tumors, the main cause of acromegaly. This review will summarize the current knowledge regarding EMT and SRLs resistance in acromegaly and, based on this relation, will suggest new biomarkers and possible therapies to SRLs resistant tumors.

Significance of Crooke's Hyaline Change in Nontumorous Corticotrophs of Patients With Cushing Disease

BACKGROUND

Glucocorticoid excess in Cushing disease (CD) leads to negative feedback suppression, resulting in Crooke's hyaline change (CC) of nontumorous pituitary corticotrophs. We aimed to determine the predictive value of CC of nontumorous corticotrophs in CD.

METHODS

The retrospective chart review study included patients with clinical, biochemical, radiologic and outcome data and evaluable histopathology specimens from pituitary surgery for CD. The main outcome was remission of CD, defined by clinical features, biochemical testing, and corticosteroid dependency.

RESULTS

Of 144 CD patients, 60 (50 women, mean age 43.6±14) had clinical follow-up, biochemical data and histopathology specimens that included evaluable nontumorous adenohypophysis. Specimens from 50 patients (83.3%) demonstrated CC in nontumorous corticotrophs, and 10 (16.7%) had no CC (including 3 with corticotroph hyperplasia). One patient with CC was lost to follow-up and one without CC had equivocal outcome results. During a mean (SD) follow-up period of 74.9 months (61.0), recurrent or persistent disease was documented in 18 patients (31.0%), while 40 (69.0%) were in remission. In patients with CC, the remission rate was 73.5% (95% CI, 59.7%-83.7%) (36/49), whereas it was 44.4% (95% CI, 18.9%-73.3%) (4/9) in patients with no CC. The combination of serum cortisol >138 nmol/L within a week of surgery coupled with absence of nontumorous CC greatly improved the prediction of recurrent or persistent disease.

CONCLUSIONS

CC of nontumorous corticotrophs was observed in 83% of patients with CD, and most patients with CC experienced remission. Absence of CC in nontumorous corticotrophs may serve as a predictor of reduced remission in patients with CD.

Proposal of a clinically relevant working classification of pituitary neuroendocrine tumors based on pituitary transcription factors

The immunohistochemistry (IHC) characterization of pituitary transcription factors (PTFs) PIT1, TPIT, and SF1, which enable the identification of three different adenohypophyseal cell lines, has been incorporated into the latest classification system of the World Health Organization (WHO) for pituitary adenomas. This change overturns the concept of the adenoma as solely a hormone producer and classifies these tumors based on their cell lineage. The aim of the study was to provide a diagnostic algorithm, based on IHC expression of hypophyseal hormones with potential use in diagnostic practice, contributing to an improved classification of pituitary adenomas. Our sample included 146 pituitary adenomas previously classified based on hormonal subtypes by IHC (former 2004 WHO criteria) and re-evaluated after the IHC quantification of PIT1, TPIT, and SF1 expression, under WHO 2017 recommendations. We assessed the correlation between expression of PTFs and the classification as per hormonal IHC and correlated clinicopathological profiles based on PTFs. The IHC study of PTFs allowed reclassification of 82% of tumors that were negative for all pituitary hormones, with 21 positive cases for SF1 (reclassified as gonadotroph tumors), 1 positive case for TPIT (reclassified as a corticotroph tumor), and 4 positive cases for PIT1. Using SF1 enabled detection of a substantial portion of gonadotroph tumors, reducing the estimated prevalence of null cell tumors to less than 5%, and identification of plurihormonal pituitary neuroendocrine tumors with PIT1-SF1 coexpression and hormone-negative PIT1s, a group in which we did not observe differences in the clinical behavior compared with the rest of the tumors of the same cell lineage.Our results suggest that applying a diagnostic algorithm based on the study of PTFs could contribute to improving the classification of pituitary adenomas. By adding TPIT assessment, we propose a two-step algorithm, with hypophyseal hormones being used in a selective modality, depending on initial results.

Cytokeratin profiles in pituitary neuroendocrine tumors

The presence and patterns of keratins are critical in the classification of pituitary neuroendocrine tumors. A large body of literature has included information about the staining patterns of pituitary tumors and tissues with the CAM 5.2 antibody. During an antibody validation for clinical use, we carried out staining of a series of 29 surgically resected pituitary cases containing 31 pituitary neuroendocrine tumors that were tested for CAM 5.2 as well as for cytokeratin (CK) 7, 18, 19, and 20 and the pan-keratin cocktail AE1/AE3. The results showed an almost identical staining pattern for CK18 and CAM 5.2; however, CAM 5.2 yielded more intense staining, whereas CK18 provided more delicate results. Staining results using AE1/AE3 were satisfactory but generally less intense; however, this marker was more specific, identifying keratin expression in one tumor that was negative with CAM 5.2. CK19 is expressed in nontumorous adenohypophysis but was less frequently positive in tumors; somatotroph and corticotroph tumors were negative for CK19, but CK19 antibody highlighted follicular cells in some gonadotroph tumors. CK7 and CK20 were negative in all pituitary tissues tested. Our findings underscore the role for CAM 5.2 and CK18 as the most valuable to identify specific alterations in adenohypophysial cells and their tumors; there is also a role for AE1/AE3 to verify the epithelial nature of pituitary neuroendocrine tumors that are negative for CAM 5.2 and CK18.

Genetic and Epigenetic Causes of Pituitary Adenomas

Pituitary adenomas (PAs) can be classified as non-secreting adenomas, somatotroph adenomas, corticotroph adenomas, lactotroph adenomas, and thyrotroph adenomas. Substantial advances have been made in our knowledge of the pathobiology of PAs. To obtain a comprehensive understanding of the molecular biological characteristics of different types of PAs, we reviewed the important advances that have been made involving genetic and epigenetic variation, comprising genetic mutations, chromosome number variations, DNA methylation, microRNA regulation, and transcription factor regulation. Classical tumor predisposition syndromes include multiple endocrine neoplasia type 1 (MEN1) and type 4 (MEN4) syndromes, Carney complex, and X-LAG syndromes. PAs have also been described in association with succinate dehydrogenase-related familial PA, neurofibromatosis type 1, and von Hippel-Lindau, DICER1, and Lynch syndromes. Patients with aryl hydrocarbon receptor-interacting protein (AIP) mutations often present with pituitary gigantism, either in familial or sporadic adenomas. In contrast, guanine nucleotide-binding protein G(s) subunit alpha (GNAS) and G protein-coupled receptor 101 (GPR101) mutations can lead to excess growth hormone. Moreover, the deubiquitinase gene USP8, USP48, and BRAF mutations are associated with adrenocorticotropic hormone production. In this review, we describe the genetic and epigenetic landscape of PAs and summarize novel insights into the regulation of pituitary tumorigenesis.