Plurihormonal Pituitary Tumor of Pit-1 and SF-1 Lineages, with Synchronous Collision Corticotroph Tumor: a Possible Stem Cell Phenomenon

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.

Co-expression of multiple transcription factors is associated with clinical features and endocrine prognosis in growth hormone-secreting pituitary adenomas

BACKGROUND

The types of growth hormone-secreting pituitary adenomas are diverse, we have found that there are significant differences in clinical features and prognosis between PIT-1 single-cell spectrum growth hormone adenomas and growth hormone phenotypic polyhormonal adenomas.

METHODS

This study examined a cohort of 193 patients with growth hormone-secreting pituitary adenoma (GHPA), stratifying them into two groups: PIT-1 single transcription factor positive growth hormone adenoma (STF-GHPA) and Multiple transcription factor-positive growth hormone-secreting adenomas (MTF-GHPA). The objective was to compare these two groups' clinical characteristics. Within the MTF-GHPA group, we further subtyped them based on transcription factors to evaluate potential variations in clinical manifestations. Logistic regression analyses were employed to develop a risk factor model for investigating factors influencing hormone remission.

RESULTS

There were no statistically significant differences in terms of age, gender, serum GH, and IGF-1 levels between patients diagnosed with MTF-GHPA and STF-GHPA. However, patients with MTF-GHPA exhibited a higher proportion of hypopituitarism compared to those with STF-GHPA. Furthermore, MTF-GHPA were characterized by smaller tumor size and less invasiveness, as indicated by lower Knosp classes. However, patients with MTF-GHPA have a lower rate of hormonal remission (30.8%) and more postoperative complications (31.0%), which means that STF-GHPA (hormonal remission:71.6%; postoperative complications:13.4%) has a better endocrine outcome than MTF-GHPA patients. Between the PIT-1 + SF-1+ and PIT-1 + TPIT+ subtypes within MTF-GHPA, significant differences were also observed in tumor size, endocrine outcomes, and postoperative complications. Risk factors influencing hormonal remission for GHPA included preoperative GH level, primary/recurrent, extent of resection, and transcription factor expression.

CONCLUSION

Co-expression of multiple transcription factors is an important factor associated with clinical behavior and endocrine outcomes in patients with GHPA.

Practical approaches to diagnosing PitNETs/adenomas based on cell lineage

The evolution of classification systems of pituitary adenomas (now PitNETs) has culminated in the use of transcription factor (TF) immunohistochemistry (IHC), forming a cell lineage-based system. However, several issues remain to be addressed, including the additional financial and logistic burden of undertaking the complete array of anterior pituitary hormones and TF IHC. To that end, several groups have suggested algorithms to minimise the number of tests performed, with varying levels of diagnostic accuracy. Although the proportion of null cell tumours has decreased following the use of TFs, "multilineage" tumours have been reported and characterised using transcriptomic signatures, most prominently the PIT1-SF1 co-expressing PitNETs, which do not bear a position in the present system of classification. In this review, we examine the proposed practical approaches to the diagnosis of PitNETs. We review the literature on reported PitNET types that challenge the existing classification system, such as those that express multiple TFs, with their potential clinical implications. Finally, we assess limitations in the present system, such as the lack of a standardised system for IHC interpretation, that need to be addressed in the future.

Clinicopathologic Correlates of PIT1 and SF1-Multilineage Pituitary Neuroendocrine Tumors and the Diagnostic Utility of NKX2.2 Immunohistochemistry in Pituitary Pathology

CONTEXT.—

PIT1 and SF1-multilineage pituitary neuroendocrine tumors (PitNETs) have been defined since the classification of adenohypophysial tumors based on the PIT1, SF1, and TPIT transcription factors.

OBJECTIVE.—

To describe the clinicopathologic features of PIT1 and SF1-multilineage PitNETs and to contribute to the pituitary pathology practice by questioning the expression of NKX2.2 in PitNETs.

DESIGN.—

We reviewed 345 PitNETs and described the clinicopathologic features of 8 PIT1 and SF1-multilineage tumors. NKX2.2 positivity and staining pattern were compared to those of 45 PitNETs from the control group.

RESULTS.—

PIT1 and SF1-multilineage PitNET patients had a mean age of 41.13 (range, 14-58 years) and a mean tumor diameter of 14.0 mm (range, 8-20 mm). The most common clinical presentation was acromegaly (6 of 8), and postoperative remission was achieved in all patients. On histomorphologic examination, a pseudopapillary pattern was seen in 5 of the tumors, either focally or diffusely. In addition to PIT1 and SF1, there was a diffuse staining with growth hormone and a predominantly perinuclear staining with cytokeratin 18. With NKX2.2, all multilineage tumors were positive, of which 5 were diffuse and 3 were focal. In the control group, 8 tumors (8 of 45) were positive, of which only 1 was diffuse and 7 were focal.

CONCLUSIONS.—

In conclusion, NKX2.2 is a transcription factor that can be used as an additional tool in pituitary pathology, and PIT1 and SF1-multilineage PitNETs are specific tumors that usually present with acromegaly, show signs of a nonaggressive clinical course, have a pseudopapillary histomorphology, and express NKX2.2.

High level of aneuploidy and recurrent loss of chromosome 11 as relevant features of somatotroph pituitary tumors

BACKGROUND

Somatotroph neuroendocrine pituitary tumors (sPitNET) are a subtype of pituitary tumors that commonly cause acromegaly. Our study aimed to determine the spectrum of DNA copy number abnormalities (CNAs) in sPitNETs and their relevance.

METHODS

A landscape of CNAs in sPitNETs was determined using combined whole-genome approaches involving low-pass whole genome sequencing and SNP microarrays. Fluorescent in situ hybridization (FISH) was used for microscopic validation of CNAs. The tumors were also subjected to transcriptome and DNA methylation analyses with RNAseq and microarrays, respectively.

RESULTS

We observed a wide spectrum of cytogenetic changes ranging from multiple deletions, recurrent chromosome 11 loss, stable genomes, to duplication of the majority of the chromosomes. The identified CNAs were confirmed with FISH. sPitNETs with multiple duplications were characterized by intratumoral heterogeneity in chromosome number variation in individual tumor cells, as determined with FISH. These tumors were separate CNA-related sPitNET subtype in clustering analyses with CNA signature specific for whole genome doubling-related etiology. This subtype encompassed GNAS-wild type, mostly densely granulated tumors with favorable expression level of known prognosis-related genes, notably enriched with POUF1/NR5A1-double positive PitNETs. Chromosomal deletions in sPitNETs are functionally relevant. They occurred in gene-dense DNA regions and were related to genes downregulation and increased DNA methylation in the CpG island and promoter regions in the affected regions. Recurrent loss of chromosome 11 was reflected by lowered MEN1 and AIP. No such unequivocal relevance was found for chromosomal gains. Comparisons of transcriptomes of selected most cytogenetically stable sPitNETs with tumors with recurrent loss of chromosome 11 showed upregulation of processes related to gene dosage compensation mechanism in tumors with deletion. Comparison of stable tumors with those with multiple duplications showed upregulation of processes related to mitotic spindle, DNA repair, and chromatin organization. Both comparisons showed upregulation of the processes related to immune infiltration in cytogenetically stable tumors and deconvolution of DNA methylation data indicated a higher content of specified immune cells and lower tumor purity in these tumors.

CONCLUSIONS

sPitNETs fall into three relevant cytogenetic groups: highly aneuploid tumors characterized by known prognostically favorable features and low aneuploidy tumors including specific subtype with chromosome 11 loss.

A Non-Secreting Pituitary Adenoma That Changed to a Prolactinoma

Pituitary adenomas (PAs) are the third most common brain tumors in adults right after meningiomas and gliomas. Taking into account their hormonal activity in vivo, they can be divided in functioning PAs, which secrete hormones, and nonfunctioning pituitary adenomas (NFPAs), which are not associated with increased hormone secretion. We present the case of a man diagnosed with pituitary apoplexy. A transsphenoidal surgery was performed with subtotal removal of the mass. Pituitary hormones were measured before and after the procedure on several occasions, showing always normal PRL values, so he was diagnosed with a clinically NFPA. Two years later, the patient noticed a visual deficit. A new magnetic resonance imaging study was performed, showing adenomatous recurrence, and the patient underwent a new surgery. After this, hormonal evaluation revealed high levels of PRL on several occasions. After treatment with cabergoline was started, PRL levels normalized, the visual deficit improved, and there was a slight adenoma reduction. This case report represents an exception to the paradigm that in the presence of a macroadenoma and normal PRL levels (avoiding the "hook effect"), a prolactinoma can be discarded. Moreover, it stresses the importance of comprehensive, regular, and lifelong surveillance of patients with NFPAs and the close monitoring of serum PRL.

Pituitary tumours without distinct lineage differentiation express stem cell marker SOX2

CONTEXT

The recent WHO 2022 Classification of pituitary tumours identified a novel group of 'plurihormonal tumours without distinct lineage differentiation (WDLD)'. By definition, these express multiple combinations of lineage commitment transcription factors, in a monomorphous population of cells.

OBJECTIVES

To determine the expression of stem cell markers (SOX2, Nestin, CD133) within tumours WDLD, immature PIT-1 lineage and acidophil stem cell tumours, compared with committed cell lineage tumours.

METHODS

Retrospective evaluation of surgically resected pituitary tumours from St Vincent's Hospital, Sydney. Patients were selected to cover a range of tumour types, based on transcription factor and hormone immunohistochemistry. Clinical data was collected from patient files. Radiology reports were reviewed for size and invasion. Samples were analysed by immunohistochemistry and RT-qPCR for SF-1, PIT-1, T-PIT, SOX2, Nestin and CD133. Stem cell markers were compared between tumours WDLD and those with classically "mature" types.

RESULTS

On immunohistochemistry, SOX2 was positive in a higher proportion of tumours WDLD compared with those meeting WHO lineage criteria, 7/10 v 10/42 (70 v 23.4%, p = 0.005). CD133 was positive in 2/10 tumours WDLD but 0/41 meeting lineage criteria, P = 0.003. On RT-qPCR, there was no significant difference in relative expression of stem cell markers (SOX2, CD133, Nestin) between tumours with and WDLD.

CONCLUSIONS

Our study is the first to biologically characterise pituitary tumours WDLD. We demonstrate that these tumours exhibit a higher expression of the stem cell marker SOX2 compared with other lineage-differentiated tumours, suggesting possible involvement of stem cells in their development.

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.

Phenotype Transformation of PitNETs

Phenotype transformation in pituitary neuroendocrine tumors is a little-known and unpredictable clinical phenomenon. Previous studies have not clearly defined and systematically concluded on the causes of this rare phenomenon. Additionally, the mechanisms of phenotype transformation are not well known. We reviewed cases reported in the literature with the aim of defining phenotype transformation in pituitary neuroendocrine tumors. We present an overview of the wide spectrum of phenotype transformation and its clinical features. We also discuss findings on the potential mechanism of this rare transformation, which may be related to PC1/3, the bioactivity of secretory hormones, gene mutations and the plasticity of pituitary neuroendocrine tumors. Clinicians should be aware of this rare phenomenon and more studies on the underlying mechanisms are required.

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.

Clinical and Pathological Features of Pit1/SF1 Multilineage Pituitary Neuroendocrine Tumor

BACKGROUND AND OBJECTIVES

Lineage-based classification has critical clinical implications in pituitary neuroendocrine tumor (PitNET). As the most prevalent subtype of multilineage PitNET, PitNET originating from both pituitary-specific positive transcription factor 1 (Pit1) and steroidogenic factor-1 (SF1) lineages (Pit1/SF1-adenoma) is expected to exhibit rich and varied clinical behaviors. A comprehensive understanding of the clinical and pathological characteristics of Pit1/SF1-adenoma will provide mechanistic insight and influence the prognosis and treatment of PitNET.

METHODS

A retrospective study was conducted by reviewing 57 cases of Pit1/SF1-adenoma between 2018 and 2022. We also included 88 cases of PitNET arising from Pit1 cell lineage (Pit1-adenoma) and 70 cases of PitNET arising from SF1 cell lineage (SF1-adenoma) as controls. Comprehensive data, including demographic, symptom, endocrinal, radiological, surgical, pathological, and prognostic information, were systematically collected. All specimens were immunostained for pituitary transcription factors (PTFs) and pituitary hormones.

RESULTS

The detection rate was 8.0% for Pit1/SF1-adenoma within PitNET surgical specimens. Pit1/SF1-adenoma displayed a male predominance, with the mean diagnosis age falling between Pit1-adenoma and SF1-adenoma. The endocrine activity of Pit1/SF1-adenoma was lower than Pit1-adenoma but higher than SF1-adenoma. Pit1/SF1-adenoma had a higher incidence of cavernous sinus invasion (56.1%) than both Pit1-adenoma (38.6%, P = .039) and SF1-adenoma (27.1%, P = .001). Furthermore, Pit1/SF1-adenoma showed more postoperative complications than Pit1-adenoma (29.8% vs 8.0%, P = .001). Nonfunctional Pit1/SF1-adenoma had a higher radiological tumor recurrence rate than nonfunctional SF1-adenoma (34.8% vs 10.9%, P = .021). Notably, the immunostaining pattern was diverse in Pit1/SF1-adenoma, with various combinations of staining intensity for PTFs and 15 combinations for 6 pituitary hormones. Intriguingly, various PTFs combinations had no different impact on the outcome of Pit1/SF1-adenoma.

CONCLUSION

Pit1/SF1-adenoma represents a unique pathological subtype of PitNET, characterized by distinctive clinical behaviors. Identifying Pit1/SF1-adenoma can facilitate more precise management of PitNET by the practical use of Pit1/SF1 immunostaining.

Single-Cell Transcriptomics Identifies Pituitary Gland Changes in Diet-Induced Obesity in Male Mice

Obesity is a chronic disease with increasing prevalence worldwide. Obesity leads to an increased risk of heart disease, stroke, and diabetes, as well as endocrine alterations, reproductive disorders, changes in basal metabolism, and stress hormone production, all of which are regulated by the pituitary. In this study, we performed single-cell RNA sequencing of pituitary glands from male mice fed control and high-fat diet (HFD) to determine obesity-mediated changes in pituitary cell populations and gene expression. We determined that HFD exposure is associated with dramatic changes in somatotrope and lactotrope populations, by increasing the proportion of somatotropes and decreasing the proportion of lactotropes. Fractions of other hormone-producing cell populations remained unaffected. Gene expression changes demonstrated that in HFD, somatotropes became more metabolically active, with increased expression of genes associated with cellular respiration, and downregulation of genes and pathways associated with cholesterol biosynthesis. Despite a lack of changes in gonadotrope fraction, genes important in the regulation of gonadotropin hormone production were significantly downregulated. Corticotropes and thyrotropes were the least affected in HFD, while melanotropes exhibited reduced proportion. Lastly, we determined that changes in plasticity and gene expression were associated with changes in hormone levels. Serum prolactin was decreased corresponding to reduced lactotrope fraction, while lower luteinizing hormone and follicle-stimulating hormone in the serum corresponded to a decrease in transcription and translation. Taken together, our study highlights diet-mediated changes in pituitary gland populations and gene expression that play a role in altered hormone levels in obesity.

Pathogenesis, clinical features, and treatment of plurihormonal pituitary adenoma

Plurihormonal pituitary adenoma (PPA) is a type of pituitary tumor capable of producing two or more hormones and usually presents as an aggressive, large adenoma. As yet, its pathogenesis remains unclear. This is the first study to systematically summarize the underlying pathogenesis of PPA. The pathogenesis is related to plurihormonal primordial stem cells, co-transcription factors, hormone co-expression, differential gene expression, and cell transdifferentiation. We conducted a literature review of PPA and analyzed its clinical characteristics. We found that the average age of patients with PPA was approximately 40 years, and most showed only one clinical symptom. The most common manifestation was acromegaly. Currently, PPA is treated with surgical resection. However, recent studies suggest that immunotherapy may be a potentially effective treatment.

DNA Methylation Pattern in Somatotroph Pituitary Neuroendocrine Tumors

INTRODUCTION

Growth hormone secretion by sporadic somatotroph neuroendocrine pituitary tumors (PitNETs) is a major cause of acromegaly. These tumors are relatively heterogenous in terms of histopathological and molecular features. Our previous transcriptomic profiling of somatotroph tumors revealed three distinct molecular subtypes. This study aimed to investigate the difference in DNA methylation patterns in subtypes of somatotroph PitNETs and its role in distinctive gene expression.

METHODS

Genome-wide DNA methylation was investigated in 48 somatotroph PitNETs with EPIC microarrays. Gene expression was assessed with RNAseq. Bisulfite pyrosequencing and qRT-PCR were used for verifying the results of DNA methylation and gene expression.

RESULTS

Clustering tumor samples based on methylation data reflected the transcriptome-related classification. Subtype 1 tumors are densely granulated without GNAS mutation, characterized by high expression of NR5A1 (SF-1) and GIPR. The expression of both genes is correlated with specific methylation of the gene body and promoter. This subtype has a lower methylation level of 5' gene regions and CpG islands than the remaining tumors. Subtype 2 PitNETs are densely granulated and frequently GNAS-mutated, while those in subtype 3 are mainly sparsely granulated. Methylation/expression analysis indicates that ∼50% genes located in differentially methylated regions are those differentially expressed between tumor subtypes. Correlation analysis revealed DNA methylation-controlled genes, including CDKN1B, CCND2, EBF3, CDH4, CDH12, MGMT, STAT5A, PLXND1, PTPRE, and MMP16, and genes encoding ion channels and semaphorins.

CONCLUSION

DNA methylation profiling confirmed the existence of three molecular subtypes of somatotroph PitNETs. High expression of NR5A1 and GIPR in subtype 1 tumors is correlated with specific methylation of both genes.

Non-coding RNAs and exosomal non-coding RNAs in pituitary adenoma

Pituitary adenoma (PA) is the third most common primary intracranial tumor in terms of overall disease incidence. Although they are benign tumors, they can have a variety of clinical symptoms, but are mostly asymptomatic, which often leads to diagnosis at an advanced stage when surgical intervention is ineffective. Earlier identification of PA could reduce morbidity and allow better clinical management of the affected patients. Non-coding RNAs (ncRNAs) do not generally code for proteins, but can modulate biological processes at the post-transcriptional level through a variety of molecular mechanisms. An increased number of ncRNA expression profiles have been found in PAs. Therefore, understanding the expression patterns of different ncRNAs could be a promising method for developing non-invasive biomarkers. This review summarizes the expression patterns of dysregulated ncRNAs (microRNAs, long non-coding RNAs, and circular RNAs) involved in PA, which could one day serve as innovative biomarkers or therapeutic targets for the treatment of this neoplasia. We also discuss the potential molecular pathways by which the dysregulated ncRNAs could cause PA and affect its progression.

Novel Candidate Regulators and Developmental Trajectory of Pituitary Thyrotropes

The pituitary gland regulates growth, metabolism, reproduction, the stress response, uterine contractions, lactation, and water retention. It secretes hormones in response to hypothalamic input, end organ feedback, and diurnal cues. The mechanisms by which pituitary stem cells are recruited to proliferate, maintain quiescence, or differentiate into specific cell types, especially thyrotropes, are not well understood. We used single-cell RNA sequencing in juvenile P7 mouse pituitary cells to identify novel factors in pituitary cell populations, with a focus on thyrotropes and rare subtypes. We first observed cells coexpressing markers of both thyrotropes and gonadotropes, such as Pou1f1 and Nr5a1. This was validated in vivo by both immunohistochemistry and lineage tracing of thyrotropes derived from Nr5a1-Cre; mTmG mice and demonstrates that Nr5a1-progenitors give rise to a proportion of thyrotropes during development. Our data set also identifies novel factors expressed in pars distalis and pars tuberalis thyrotropes, including the Shox2b isoform in all thyrotropes and Sox14 specifically in Pou1f1-negative pars tuberalis thyrotropes. We have therefore used single-cell transcriptomics to determine a novel developmental trajectory for thyrotropes and potential novel regulators of thyrotrope populations.

An Overview of Pituitary Neuroendocrine Tumors (PitNET) and Algorithmic Approach to Diagnosis

The diagnostic algorithm and nomenclature of pituitary neuroendocrine tumors have evolved over the past decade, beginning with simpler categorical schemes focused on histomorphologic features and moving to a more sophisticated lineage-specific categorization. This contemporary overview highlights a multimodal approach to pituitary neuroendocrine tumors with a focus on changes in nomenclature, classification, and subclassification; including, brief comments on treatment, and new guidelines for genetic screening, particularly for young patients with such neoplasms.

Development of a cost-effective diagnostic algorithm incorporating transcription factor immunohistochemistry in the evaluation of pituitary tumours

PURPOSE

To determine the utility of the 2022 WHO Classification of pituitary tumours in routine clinical practice and to develop an optimal diagnostic algorithm for evaluation of tumour type in a real-world setting.

METHODS

Retrospective evaluation of pituitary tumour immunohistochemistry (IHC), operatively managed at St Vincent's Hospital Sydney, between 2019 and 2021. Routine IHC comprised evaluation of transcription factors [steroidogenic factor 1 (SF1), T-box transcription factor 19 (TPIT) and pituitary-specific positive transcription factor (PIT1)] and anterior pituitary hormones. Three tiered algorithms were tested, in which hormone IHC was performed selectively based on the initial transcription factor results. These were applied retrospectively and compared with current practice 'gold standard' comprising all transcription factor and hormone IHC. Diagnostic accuracy and cost were evaluated for each.

RESULTS

There were 113 tumours included in the analysis. All three algorithms resulted in 100% concordance with the 'gold standard' in the characterisation of tumour lineage. While all three were associated with relative cost reduction, Algorithm #3, which omitted hormone IHC in the setting of positive SF1 or TPIT and performed IHC for growth hormone, prolactin and thyroid stimulating hormone only in the setting of PIT1 positivity, was the most cost-efficient. Additionally, there were 12/113 tumours with no distinct cell lineage.

CONCLUSION

A diagnostic algorithm omitting hormone IHC except in cases of PIT1 positivity is an accurate and cost-effective approach to diagnose the type of pituitary tumour. A significant subgroup of pituitary tumours with no distinct cell lineage, frequently plurihormonal, remains difficult to classify with the new WHO criteria and requires further evaluation.

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.

Pituitary neuroendocrine tumors: a model for neuroendocrine tumor classification

The classification of adenohypophysial neoplasms as "pituitary neuroendocrine tumors" (PitNETs) was proposed in 2017 to reflect their characteristics as epithelial neuroendocrine neoplasms with a spectrum of clinical behaviors ranging from small indolent lesions to large, locally invasive, unresectable tumors. Tumor growth and hormone hypersecretion cause significant morbidity and mortality in a subset of patients. The proposal was endorsed by a WHO working group that sought to provide a unified approach to neuroendocrine neoplasia in all body sites. We review the features that are characteristic of neuroendocrine cells, the epidemiology and prognosis of these tumors, as well as further refinements in terms used for other pituitary tumors to ensure consistency with the WHO framework. The intense study of PitNETs has provided information about the importance of cellular differentiation in tumor prognosis as a model for neuroendocrine tumors in different locations.

An Update on Pituitary Neuroendocrine Tumors Leading to Acromegaly and Gigantism

An excess of growth hormone (GH) results in accelerated growth and in childhood, the clinical manifestation is gigantism. When GH excess has its onset after epiphyseal fusion at puberty, the overgrowth of soft tissue and bone results in acromegaly. Persistent GH excess in gigantism also causes acromegalic features that become evident in the adult years. The causes of GH excess are primarily lesions in the pituitary, which is the main source of GH. In this review, we provide an update on the clinical, radiological and pathologic features of the various types of pituitary neuroendocrine tumors (PitNETs) that produce GH. These tumors are all derived from PIT1-lineage cells. Those composed of somatotrophs may be densely granulated, resembling normal somatotrophs, or sparsely granulated with unusual fibrous bodies. Those composed of mammosomatotrophs also produce prolactin; rare plurihormonal tumors composed of cells that resemble mammosomatotrophs also produce TSH. Some PitNETs are composed of immature PIT1-lineage cells that do not resemble differentiated somatotrophs, mammosomatotrophs, lactotroph or thyrotrophs; these tumors may cause GH excess. An unusual oncocytic PIT1-lineage tumor known as the acidophil stem cell tumor is predominantly a lactotroph tumor but may express GH. Immature PIT1-lineage cells that express variable amounts of hormones alone or in combination can sometimes cause GH excess. Unusual tumors that do not follow normal lineage differentiation may also secrete GH. Exceptional examples of acromegaly/gigantism are caused by sellar tumors composed of hypothalamic GHRH-producing neurons, alone or associated with a sparsely granulated somatotroph tumor. Each of these various tumors has distinct clinical, biochemical and radiological features. Data from careful studies based on morphologic subtyping indicate that morphologic classification has both prognostic and predictive value.

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.

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

The traditional approach to the diagnosis of primary adenohypophyseal cell proliferations uses hormone immunohistochemistry to classify pituitary neuroendocrine tumors (PitNETs). The routine application of immunolocalization of pituitary transcription factors (SF1, PIT1, TPIT, ERα, and recently GATA3) along with adenohypophyseal hormones has taught us critical lessons that are discussed in this communication. We point out that appropriate patient care requires accurate diagnosis and is critical in the era of precision medicine. A misdiagnosis can result in far greater health care costs than the cost of accurate tumor classification and may have other unintended consequences. We provide additional insights about confusing findings in genomic studies, emphasizing that high-quality pathology is essential for strong science and translational research.

Comprehensive circular RNA profiling reveals that hsa_circ_0001368 is involved in growth hormone-secreting pituitary adenoma development

Growth hormone-secreting pituitary adenoma (GHPA) represents about 20% of all histological subtypes of pituitary adenoma (PA), which may result in serious complications and shortened lifespan via growth-hormone (GH) hypersecretion. To date, no biomarkers of early diagnosis or therapeutic targets for GHPA treatment have yet been found. Recently, growing evidence has indicated that circular RNAs (circRNAs) are critical for the development and progression of numerous diseases, including cancers; however, their role in the pathogenesis of GHPA has not been reported. Here, we revealed the expression profile of circRNAs in GHPA using a circRNA microarray, and found 1938 circRNAs were upregulated and 1601 circRNAs were downregulated in GHPA versus normal control. Then the ten most up-regulated circRNAs were selected for the mapping of a circRNA-miRNA-target gene interaction network. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses further indicate that target genes were mostly enriched in the mTOR and the Wnt signaling pathway. Among these differentially expressed circRNAs, hsa_circ_0001368 was verified significant up-regulated by qRT-PCR, which was specific up-regulated in GHPA and correlated with the invasiveness and serum GH level of GHPA; functional studies indicated that knockdown of hsa_circ_0001368 significantly inhibited the proliferation, invasion and GH secreting level of GHPA primary culture cells. Moreover, hsa_circ_0001368 had a significant positive correlation with the pituitary-specific transcription factor Pit-1. In conclusion, our study identified a wealth of candidate circRNAs involved in GHPA and proposed that hsa_circ_0001368 may represent a novel potential biomarker and therapeutic target of GHPA.

Pituitary Adenomas with Changing Phenotype: A Systematic Review

PURPOSE AND METHODS

Phenotype transformation in pituitary adenomas (PA) is a little known and unexpected clinical phenomenon. We describe two illustrative cases and performed a systematic review of cases reported in literature.

RESULTS

Case 1: A 24-year-old woman underwent surgery because of Cushing's disease. A complete tumor resection and hypercortisolism resolution was achieved. Two years later, tumor recurred but clinical and hormonal hypercortisolism were absent. Case 2: A 77-year-old woman underwent surgery due to acromegaly. A complete tumor resection and GH excess remission was achieved. Four years later, tumor recurred but clinical and hormonal acromegaly was ruled out. Search of literature: From 20 patients (including our cases), 75% were female with median age 45 (19) years. Ten patients (50%) had initially functioning PA: 8 switched to NFPA (5 ACTH-secreting PA, 2 prolactinomas and 1 acromegaly) and 2 exchanged to acromegaly from TSH-secreting PA and microprolactinoma. One patient developed a pituitary carcinoma from ACTH-secreting PA. Ten patients (50%) initially had NFPA; 9 developed Cushing's disease (4 silent corticotroph adenomas, 4 null cell PA and 1 managed conservatively). One patient with silent somatotroph PA changed to acromegaly. Treatments before transformation were surgery (80%), radiotherapy (40%), pharmacological (40%) and in 2 patients switching happened without any treatment. Median follow-up until transformation was 72 months (range 12-276).

CONCLUSION

PA can change from functioning to (NF) non-functioning (vice versa) and even exchange their hormonal expression. Clinicians should be aware and a careful lifelong follow-up is mandatory to detect it.

TWO SYNCHRONOUS PITUITARY ADENOMAS CAUSING CUSHING DISEASE AND ACROMEGALY

OBJECTIVE

To report the first case of 2 synchronous pituitary adenomas, 1 corticotroph and 1 somatotroph, with distinct molecular lineages confirmed by differential hormone and S-100 protein expression.

METHODS

A case report followed by a literature review are presented.

RESULTS

A 68-year-old woman presented for evaluation of resistant hypertension. Biochemical testing demonstrated adrenocorticotropic hormone (ACTH)-dependent hypercortisolemia and growth hormone (GH) excess. Pituitary magnetic resonance imaging (MRI) revealed a 2 cm left sellar lesion consistent with a pituitary macroadenoma. The patient therefore underwent transsphenoidal surgery for a presumed cosecreting ACTH and GH macroadenoma. Tumor immunohistochemical staining (IHC) was positive for ACTH, but negative for GH. Postoperative biochemical testing confirmed remission from Cushing disease, but the insulin-like growth factor 1 (IGF-1) level remained elevated. Postoperative MRI demonstrated a small right sellar lesion that, in retrospect, had been present on the preoperative MRI. Resection of the right lesion confirmed a GH-secreting adenoma with negative ACTH staining. After the second surgery, the IGF-1 level normalized and blood pressure improved. Further pathologic examination of both surgical specimens demonstrated differential expression of S-100 protein, a folliculostellate cell marker. Reverse transcription polymerase chain reaction of messenger ribonucleic acid from the left sellar lesion was positive for ACTH and negative for GH, confirming the IHC results. Germline mutations in genes known to be associated with pituitary adenoma syndromes (MEN1, CDC73, CDKN1A, CDKN1B, CDKN2B, CDKN2C, and AIP) were not detected.

CONCLUSION

Although the pathogenesis of synchronous pituitary adenomas has not been fully elucidated, this case report suggests that they can have distinct molecular lineages.