A Novel Expression Profile of Cell Cycle and DNA Repair Proteins in Nonfunctioning Pituitary Adenomas

New insights in cellular senescence: The pituitary model

Pituitary tumors are characterized by slow proliferation rates and a high prevalence within the population. The pathogenesis of these tumors remains incompletely understood, although accumulating evidence suggests that the activation of the cellular senescence program, triggered by various stressors and functioning as a brake on cellular proliferation, may contribute to their typically benign nature. Multiple mediators of the senescence response are implicated in this process. Interleukin-6 (IL-6), a proinflammatory cytokine, plays a dual role in pituitary tumor biology. It is involved in both physiological pituitary growth and the senescence-associated secretory phenotype (SASP), where it mediates paracrine-proliferative signals. In addition to its secretory functions, IL-6 has been implicated in the regulation of pituitary senescence through non-secretory mechanisms. Other factors, such as growth hormone (GH), the pituitary tumor-transforming gene (PTTG), and interactions within the tumor microenvironment, including immune cell dynamics, also contribute to the senescence observed in these tumors. This review examines the latest evidence concerning the role of senescence in pituitary tumors, with a particular focus on the contribution of IL-6 to this process.

Increased Prevalence of Germline Pathogenic CHEK2 Variants in Individuals With Pituitary Adenomas

CONTEXT

CHEK2 is a cell cycle checkpoint regulator gene with a long-established role as a clinically relevant, moderate risk breast cancer predisposition gene, with greater risk ascribed to truncating variants than missense variants.

OBJECTIVE

To assess the rate and pathogenicity of CHEK2 variants amongst individuals with pituitary adenomas (PAs).

METHODS

We assessed 165 individuals with PAs for CHEK2 variants. The study population comprised a primary cohort of 29 individuals who underwent germline and tumor whole-exome sequencing, and a second, independent cohort of 136 individuals who had a targeted next-generation sequencing panel performed on both germline and tumor DNA (n = 52) or germline DNA alone (n = 84).

RESULTS

We identified rare, coding, nonsynonymous germline CHEK2 variants amongst 3 of 29 (10.3%) patients in our primary cohort, and in 5 of 165 (3.0%) patients overall, with affected patients having a range of PA types (prolactinoma, thyrotropinoma, somatotropinoma, and nonfunctioning PA). No somatic variants were identified. Two variants were definitive null variants (c.1100delC, c.444 + 1G > A), classified as pathogenic. Two variants were missense variants (p.Asn186His, p.Thr476Met), classified as likely pathogenic. Even when considering the null variants only, the rate of CHEK2 variants was higher in our cohort compared to national control data (1.8% vs 0.5%; P = .049).

CONCLUSION

This is the first study to suggest a role for the breast cancer predisposition gene, CHEK2, in pituitary tumorigenesis, with pathogenic/likely pathogenic variants found in 3% of patients with PAs. As PAs are relatively common and typically lack classic autosomal dominant family histories, risk alleles-such as these variants found in CHEK2-might be a significant contributor to PA risk in the general population.

Oxidative stress in pituitary neuroendocrine tumors: Affecting the tumor microenvironment and becoming a new target for pituitary neuroendocrine tumor therapy

Pituitary adenomas (PAs), or pituitary neuroendocrine tumors (PitNETs), are commonly found in the anterior pituitary gland. Although the majority of PitNETs are benign and stable, several tumors have malignant characteristics. The tumor microenvironment (TME) plays an important role in the process of tumorigenesis and is composed of several types of cells. Various cells in the TME are significantly affected by oxidative stress. It has been reported that immunotherapeutic strategies have good effects in several cancers. However, the clinical potential of immunotherapies in PitNETs has not yet been fully discussed. Oxidative stress can regulate PitNET cells and immune cells in the TME, thus affecting the immune status of the TME of PitNETs. Therefore, modulation of oxidative stress-regulated immune cells using a combination of several agents and the immune system to suppress PitNETs is a promising therapeutic direction. In this review, we systematically analyzed the oxidative stress process within PitNET cells and various immune cells to elucidate the potential value of immunotherapy.

An Update on Silent Corticotroph Adenomas: Diagnosis, Mechanisms, Clinical Features, and Management

Simple Summary

The 2017 World Health Organization classification of endocrine tumors defines pituitary adenomas based on their cell lineages. T-PIT can serve as a complimentary tool for further identification of silent corticotroph adenomas (SCAs). Unlike functioning corticotroph adenomas in patients with Cushing’s disease, SCAs present no clinical and biochemical features of Cushing’s syndrome. SCAs have been shown to exhibit a more aggressive course characterized by a higher probability of recurrence and resistance to conventional treatment due to their intrinsic histological features. The aim of our review is to offer an update on the diagnosis, mechanisms, clinical features and management of SCAs. Studies of the molecular mechanisms of SCA pathogenesis will provide new directions for the diagnosis and management of SCAs.

Abstract

With the introduction of 2017 World Health Organization (WHO) classification of endocrine tumors, T-PIT can serve as a complementary tool for identification of silent corticotroph adenomas (SCAs) in some cases if the tumor is not classifiable by pituitary hormone expression in pathological tissue samples. An increase of the proportion of SCAs among the non-functioning pituitary adenomas (NFPAs) has been witnessed under the new rule with the detection of T-PIT-positive ACTH-negative SCAs. Studies of molecular mechanisms related to SCA pathogenesis will provide new directions for the diagnosis and management of SCAs. A precise pathological diagnosis can help clinicians better identify SCAs. Understanding clinical features in the context of the pathophysiology of SCAs is critical for optimal management. It could provide information on appropriate follow-up time and aid in early recognition and treatment of potentially aggressive forms. Management approaches include surgical, radiation, and/or medical therapies.

Recurrent Acromegaly in a Patient With a CHEK2 Mutation

Background/Objective

Case Report

Discussion

Conclusion

Follicular cells in pituitary neuroendocrine tumors

Follicular cells (FCs) are thought to be agranular, non-hormone-producing stellate cells distributed throughout the adenohypophysis, occasionally arranged around colloid-filled follicles, and thought to be more prominent in the vicinity of necrosis and apoptotic cells. A distinct but similar cell type, the folliculostellate cell (FSC), is a sustentacular cell that is negative for keratins and stains for S100, GFAP, and SOX10. While several studies have examined FSCs in pituitary neuroendocrine tumors (PitNETs), the distribution and derivation of FCs in these lesions is unclear. We examined the presence and distribution of FCs in 104 PitNETs obtained by trans-sphenoidal surgery, using immunohistochemistry for keratins as well as the full complement of immunohistochemical stains for tumor characterization. The tumors included 9 somatotroph, 5 mammosomatotroph, 7 lactotroph, 7 immature PIT1-lineage, 2 acidophil stem cell, 17 corticotroph, 53 gonadotroph, 2 null cell, and 2 unusual plurihormonal tumors. CK-positive FCs were only identified in gonadotroph PitNETs and were found in 12 (23%) of those tumors; all other tumor types were negative for FCs. FCs express keratins identified by CAM5.2, AE1/AE3, CK18, and CK19 antibodies. FCs were identified scattered singly among hormone-producing neuroendocrine cells, in small clusters of 3-5 cells and surrounding colloid-filled follicles, as well as linearly along intratumoral blood vessels. Sequential stains showed that FCs express nuclear SF1 and GATA3, transcription factors of gonadotrophs, and multiplex immunohistochemistry confirmed colocalization of SF1 in the nucleus of keratin-positive FCs. In this series, FCs were exclusively found in gonadotroph PitNETs and occurred in 23% of those tumors. Co-expression of gonadotroph transcription factors in FCs supports the concept of cellular plasticity and transformation of neoplastic hormone-producing neuroendocrine cells to FCs. Further studies are required to determine if and why gonadotrophs alone undergo this transformation, the function of these cells and whether they have prognostic value.

Genomics and Epigenomics of Pituitary Tumors: What Do Pathologists Need to Know?

Molecular pathology has advanced our understanding of many tumors and offers opportunities to identify novel therapies. In the pituitary, the field has uncovered several genetic mutations that predispose to pituitary neuroendocrine tumor (PitNET) development, including MEN1, CDKN1B, PRKRIα, AIP, GPR101, and other more rare events; however, these genes are only rarely mutated in sporadic PitNETs. Recurrent genetic events in sporadic PitNETs include GNAS mutations in a subset of somatotroph tumors and ubiquitin-specific peptidase mutations (e.g., USP8, USP48) in some corticotroph tumors; to date, neither of these has resulted in altered management, and instead, the prognosis and management of PitNETs still rely more on cell type and subtype as well as local growth that determines surgical resectability. In contrast, craniopharyngiomas have either CTNNB1 or BRAF^V600E mutations that correlate with adamantinomatous or papillary morphology, respectively; the latter offers the opportunity for targeted therapy. DICER1 mutations are found in patients with pituitary blastoma. Epigenetic changes are implicated in the pathogenesis of the more common sporadic pituitary neoplasms including the majority of PitNETs and tumors of pituicytes.

Increased E2F1 mRNA and miR-17-5p Expression Is Correlated to Invasiveness and Proliferation of Pituitary Neuroendocrine Tumours

miR-17-5p and E2F1 have been described as deregulated in cancer, but they have scarcely been studied in pituitary neuroendocrine tumours (PitNETs). This study evaluates the relationship of E2F1 and miR-17-5p with the invasiveness and proliferation of PitNETs. In this cross-sectional descriptive study, we evaluated the expression of E2F1, MYC, and miR-17-5p by quantitative real time PCR analysis in 60 PitNETs: 29 gonadotroph (GT), 15 functioning somatotroph (ST), and 16 corticotroph (CT) tumours, of which 8 were silent (sCT). The clinical data were collected from the Spanish Molecular Register of Pituitary Adenomas (REMAH) database. We defined invasiveness according to the Knosp classification and proliferation according to a molecular expression of Ki-67 ≥ 2.59. E2F1 was more expressed in invasive than in non-invasive tumours in the whole series (p = 0.004) and in STs (p = 0.01). In addition, it was overexpressed in the silent subtypes (GTs and sCTs; all macroadenomas) and normoexpressed in the functioning ones (fCTs and STs; some microadenomas). miR-17-5p was more expressed in proliferative than in non-proliferative tumours (p = 0.041) in the whole series but not by subtypes. Conclusions: Our study suggests that in PitNETs, E2F1 could be a good biomarker of invasiveness, and miR-17-5p of proliferation, helping the clinical management of these tumours.