ERG gene rearrangements are common in prostatic small cell carcinomas

[Neuroendocrine prostate cancer]

Neuroendocrine prostate cancer (NEPC) mostly occurs as a treatment-emergent adaptive response under the pressure of intensive androgen deprivation treatment (t-NEPC). Approximately 30-40% of patients with metastatic castration-resistant prostate cancer (mCRPC) also have neuroendocrine involvement. In contrast primary small cell prostate cancer is very rare (<1%). A t‑NEPC should be clinically suspected in patients who have particularly aggressive mCRPC but a disproportionately low prostate-specific antigen (PSA) level and elevated neuroendocrine tumor markers, such as chromogranin A and neuron-specific enolase. The initial Gleason score was shown to be an independent factor correlated to the risk of development of t‑NEPC. Treatment is oriented to that of small cell lung cancer. In patients with negative PSA levels, chemotherapy with cisplatin and etoposide is the first line treatment, for which response rates in the range of 30-60% with a median survival time of usually less than 1 year can be achieved. In patients with much higher serum PSA levels, chemotherapy with carboplatin plus docetaxel should be considered.

The β2-Adrenergic Receptor Is a Molecular Switch for Neuroendocrine Transdifferentiation of Prostate Cancer Cells

The incidence of treatment-related neuroendocrine prostate cancer (t-NEPC) is rising as more potent drugs targeting the androgen signaling axis are clinically implemented. Neuroendocrine transdifferentiation (NEtD), an putative initial step in t-NEPC development, is induced by androgen-deprivation therapy (ADT) or anti-androgens, and by activation of the β₂-adrenergic receptor (ADRB2) in prostate cancer cell lines. Thus, understanding whether ADRB2 is involved in ADT-initiated NEtD may assist in developing treatment strategies that can prevent or reverse t-NEPC emergence, thereby prolonging therapeutic responses. Here we found that in primary, treatment-naïve prostate cancers, ADRB2 mRNA was positively correlated with expression of luminal differentiation markers, and ADRB2 protein levels were inversely correlated with Gleason grade. ADRB2 mRNA was upregulated in metastatic prostate cancer, and progressively downregulated during ADT and t-NEPC emergence. In androgen-deprivated medium, high ADRB2 was required for LNCaP cells to undergo NEtD, measured as increased neurite outgrowth and expression of neuron differentiation and neuroendocrine genes. ADRB2 overexpression induced a neuroendocrine-like morphology in both androgen receptor (AR)-positive and -negative prostate cancer cell lines. ADRB2 downregulation in LNCaP cells increased canonical Wnt signaling, and GSK3α/β inhibition reduced the expression of neuron differentiation and neuroendocrine genes. In LNCaP xenografts, more pronounced castration-induced NEtD was observed in tumors derived from high than low ADRB2 cells. In conclusion, high ADRB2 expression is required for ADT-induced NEtD, characterized by ADRB2 downregulation and t-NEPC emergence. IMPLICATIONS: This data suggest a potential application of β-blockers to prevent cancer cells committed to a neuroendocrine lineage from evolving into t-NEPC.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

BRN4 Is a Novel Driver of Neuroendocrine Differentiation in Castration-Resistant Prostate Cancer and Is Selectively Released in Extracellular Vesicles with BRN2

PURPOSE

Neuroendocrine prostate cancer (NEPC), an aggressive variant of castration-resistant prostate cancer (CRPC), often emerges after androgen receptor-targeted therapies such as enzalutamide or de novo, via trans-differentiation process of neuroendocrine differentiation. The mechanistic basis of neuroendocrine differentiation is poorly understood, contributing to lack of effective predictive biomarkers and late disease recognition. The purpose of this study was to examine the role of novel proneural Pit-Oct-Unc-domain transcription factors (TF) in NEPC and examine their potential as noninvasive predictive biomarkers.Experimental Design: Prostate cancer patient-derived xenograft models, clinical samples, and cellular neuroendocrine differentiation models were employed to determine the expression of TFs BRN1 and BRN4. BRN4 levels were modulated in prostate cancer cell lines followed by functional assays. Furthermore, extracellular vesicles (EV) were isolated from patient samples and cell culture models, characterized by nanoparticle tracking analyses, Western blotting, and real-time PCR.

RESULTS

We identify for the first time that: (i) BRN4 is amplified and overexpressed in NEPC clinical samples and that BRN4 overexpression drives neuroendocrine differentiation via its interplay with BRN2, a TF that was previously implicated in NEPC; (ii) BRN4 and BRN2 mRNA are actively released in prostate cancer EVs upon neuroendocrine differentiation induction; and (iii) enzalutamide treatment augments release of BRN4 and BRN2 in prostate cancer EVs, promoting neuroendocrine differentiation induction.

CONCLUSIONS

Our study identifies a novel TF that drives NEPC and suggests that as adaptive mechanism to enzalutamide treatment, prostate cancer cells express and secrete BRN4 and BRN2 in EVs that drive oncogenic reprogramming of prostate cancer cells to NEPC. Importantly, EV-associated BRN4 and BRN2 are potential novel noninvasive biomarkers to predict neuroendocrine differentiation in CRPC.

Lineage plasticity-mediated therapy resistance in prostate cancer

Therapy resistance is a significant challenge for prostate cancer treatment in clinic. Although targeted therapies such as androgen deprivation and androgen receptor (AR) inhibition are effective initially, tumor cells eventually evade these strategies through multiple mechanisms. Lineage reprogramming in response to hormone therapy represents a key mechanism that is increasingly observed. The studies in this area have revealed specific combinations of alterations present in adenocarcinomas that provide cells with the ability to transdifferentiate and perpetuate AR-independent tumor growth after androgen-based therapies. Interestingly, several master regulators have been identified that drive plasticity, some of which also play key roles during development and differentiation of the cell lineages in the normal prostate. Thus, further study of each AR-independent tumor type and understanding underlying mechanisms are warranted to develop combinational therapies that combat lineage plasticity in prostate cancer.

Essential Updates in Grading, Morphotyping, Reporting, and Staging of Prostate Carcinoma for General Surgical Pathologists

CONTEXT.—

Within this decade, several important updates in prostate cancer have been presented through expert international consensus conferences and influential publications of tumor classification and staging.

OBJECTIVE.—

To present key updates in prostate carcinoma.

DATA SOURCES.—

The study comprised a review of literature and our experience from routine and consultation practices.

CONCLUSIONS.—

Grade groups, a compression of the Gleason system into clinically meaningful groups relevant in this era of active surveillance and multidisciplinary care management for prostate cancer, have been introduced. Refinements in the Gleason patterns notably result in the contemporarily defined Gleason score 6 cancers having a virtually indolent behavior. Grading of tertiary and minor higher-grade patterns in radical prostatectomy has been clarified. A new classification for prostatic neuroendocrine tumors has been promulgated, and intraductal, microcystic, and pleomorphic giant cell carcinomas have been officially recognized. Reporting the percentage of Gleason pattern 4 in Gleason score 7 cancers has been recommended, and data on the enhanced risk for worse prognosis of cribriform pattern are emerging. In reporting biopsies for active surveillance criteria-based protocols, we outline approaches in special situations, including variances in sampling or submission. The 8th American Joint Commission on Cancer TNM staging for prostate cancer has eliminated pT2 subcategorization and stresses the importance of nonanatomic factors in stage groupings and outcome prediction. As the clinical and pathology practices for prostate cancer continue to evolve, it is of utmost importance that surgical pathologists become fully aware of the new changes and challenges that impact their evaluation of prostatic specimens.

Neuroendocrine Differentiation in Prostate Cancer: Emerging Biology, Models, and Therapies

Although a de novo clinical presentation of small cell neuroendocrine carcinoma of the prostate is rare, a subset of patients previously diagnosed with prostate adenocarcinoma may develop neuroendocrine features in later stages of castration-resistant prostate cancer (CRPC) progression as a result of treatment resistance. Despite sharing clinical, histologic, and some molecular features with other neuroendocrine carcinomas, including small cell lung cancer, castration-resistant neuroendocrine prostate cancer (CRPC-NE) is clonally derived from prostate adenocarcinoma. CRPC-NE therefore retains early prostate cancer genomic alterations and acquires new molecular changes making them resistant to traditional CRPC therapies. This review focuses on recent advances in our understanding of CRPC-NE biology, the transdifferentiation/plasticity process, and development and characterization of relevant CRPC-NE preclinical models.

Detection of androgen receptor (AR) and AR-V7 in small cell prostate carcinoma: Diagnostic and therapeutic implications

OBJECTIVE

Small cell prostate carcinoma (SCPC) is a rare and highly malignant subtype of prostate cancer. SCPC frequently lacks androgen receptor (AR) and prostate-specific antigen (PSA) expression, and often responds poorly to androgen deprivation therapy (ADT). AR splice variant-7 (AR-V7) is a truncated AR protein implicated in resistance to AR-targeting therapies. AR-V7 expression in castration-resistant prostate cancers has been evaluated extensively, and blood-based detection of AR-V7 has been associated with lack of response to abiraterone and enzalutamide. However, whether AR-V7 is expressed in SCPC is not known.

METHODS

Using validated antibodies, we performed immunohistochemistry (IHC) assay for the full-length AR (AR-FL) and (AR-V7) on post-ADT surgical SCPC specimens.

RESULTS

Seventy-five percent (9/12) of the specimens showed positive staining for the AR-FL with various intensities. Thirty-three percent (4/12) of the specimens showed positive staining for AR-V7. Among the specimens with positive AR-V7 staining, two samples displayed very weak staining, one sample showed weak-to-moderate staining, and one sample showed strong staining. All positive specimens displayed a heterogeneous pattern of AR-FL/AR-V7 staining. All specimens positive for AR-V7 were also positive for AR-FL.

CONCLUSION

The study findings support the existence of measurable AR-FL and AR-V7 proteins in SCPC specimens. The results also have implications in detection of AR-V7 in specimens obtained through systemic sampling approaches such as circulating tumor cells. A positive AR-V7 finding by blood-based tests is not impossible in patients with SCPC who often demonstrate low PSA values.

Morphological and Immunohistochemical Biomarkers in Distinguishing Prostate Carcinoma and Urothelial Carcinoma: A Comprehensive Review

The differential diagnosis between high-grade prostate carcinoma and infiltrating urothelial carcinoma (UC) in transurethral resection prostate specimens as well as cystoprostatectomy specimens may often be challenging due to morphologic and clinical overlap of the 2 entities. Such distinction has critical therapeutic and staging consequences, yet it is hampered by both issues in morphology and by the low accuracy rates of single immunohistochemical markers, as reported in literature. This review aims to provide a comprehensive analysis of the available morphological and immunohistochemical parameters, which may allow to discriminate between prostate carcinoma and urothelial carcinoma in the proper clinical context and to discuss their diagnostic applications in daily practice.

Complete metabolic response of metastatic castration-resistant neuroendocrine carcinoma of the prostate after treatment with RRx-001 and reintroduced platinum doublets

Presented herein is the case of a heavily pretreated patient with high-grade neuroendocrine prostate cancer that achieved a complete metabolic response on platinum-based chemotherapy after treatment with the dual CD-47 and SIRP-α inhibitor, RRx-001, in a Phase II clinical trial.

Evolving concepts in prostatic neuroendocrine manifestations: from focal divergent differentiation to amphicrine carcinoma

Prostatic neuroendocrine manifestations encompass a heterogeneous spectrum of morphologic entities. In the era of evidence-based and precision-led treatment, distinction of biologically relevant clinical manifestations expanded the evolving clinical role of pathologists. Recent observations on the occurrence of hormone therapy-induced aggressive prostatic cancers with neuroendocrine features have triggered the need to refine the spectrum and nomenclature of prostatic neuroendocrine manifestations. Although the morphologic assessment still remains the basis of the diagnostic workup of prostatic neoplasms, the application of ancillary biomarkers is crucial in the accurate classification of such presentations. This review provides a diagnostic roadmap for the practicing pathologist by reviewing the characteristic morphologic, immunohistochemical, and molecular correlates of various faces of prostatic neuroendocrine manifestations.

Molecular Biomarkers in the Clinical Management of Prostate Cancer

Prostate cancer, one of the most common noncutaneous malignancies in men, is a heterogeneous disease with variable clinical outcome. Although the majority of patients harbor indolent tumors that are essentially cured by local therapy, subsets of patients present with aggressive disease or recur/progress after primary treatment. With this in mind, modern clinical approaches to prostate cancer emphasize the need to reduce overdiagnosis and overtreatment via personalized medicine. Advances in our understanding of prostate cancer pathogenesis, coupled with recent technologic innovations, have facilitated the development and validation of numerous molecular biomarkers, representing a range of macromolecules assayed from a variety of patient sample types, to help guide the clinical management of prostate cancer, including early detection, diagnosis, prognostication, and targeted therapeutic selection. Herein, we review the current state of the art regarding prostate cancer molecular biomarkers, emphasizing those with demonstrated utility in clinical practice.

[Neuroendocrine prostate cancer]

Neuroendocrine prostate cancer (NEPC) mostly occurs as a treatment-emergent adaptive response under the pressure of intensive androgen deprivation treatment (t-NEPC). Approximately 30-40% of patients with metastatic castration-resistant prostate cancer (mCRPC) also have neuroendocrine involvement. In contrast primary small cell prostate cancer is very rare (<1%). A t‑NEPC should be clinically suspected in patients who have particularly aggressive mCRPC but a disproportionately low prostate-specific antigen (PSA) level and elevated neuroendocrine tumor markers, such as chromogranin A and neuron-specific enolase. The initial Gleason score was shown to be an independent factor correlated to the risk of development of t‑NEPC. Treatment is oriented to that of small cell lung cancer. In patients with negative PSA levels, chemotherapy with cisplatin and etoposide is the first line treatment, for which response rates in the range of 30-60% with a median survival time of usually less than 1 year can be achieved. In patients with much higher serum PSA levels, chemotherapy with carboplatin plus docetaxel should be considered.

Castration-Resistant Prostate Cancer Refractory to Second-Generation Androgen Receptor Axis-Targeted Agents: Opportunities and Challenges

Second-generation androgen receptor axis-targeted (ARAT) agents, namely abiraterone and enzalutamide, enable stronger blockade of the androgen receptor (AR) axis and longer survival of men with castration-resistant prostate cancer (CRPC). However, the extent of the improved survival remains insufficient and the majority of patients eventually develop resistance to these novel agents. Some patients develop resistance against ARAT treatment through mechanisms termed “complete AR independence” or “AR indifference”, and no longer require activation of the AR axis. However, a considerable proportion of CRPC patients remain persistently dependent on AR or its downstream signaling pathways. Ligand-independent activation of the AR, an AR axis-dependent mechanism, is mediated by truncated forms of ARs that lack the ligand-binding domain (LBD), arising as products of AR splicing variants or nonsense mutations of AR. Post-translational modifications of ARs can also contribute to ligand-independent transactivation of the AR. Other mechanisms for AR axis activation are mediated by pathways that bypass the AR. Recent studies revealed that the glucocorticoid receptor can upregulate a similar transcription program to that of the AR, thus bypassing the AR. ARAT agents are essentially ineffective for CRPC driven by these AR-independent mechanisms. This review article describes recent efforts to overcome these refractory machineries for the development of next-generation AR axis blockade in CRPC.

Genome-Based Classification and Therapy of Prostate Cancer

In the past decade, multi-national and multi-center efforts were launched to sequence prostate cancer genomes, transcriptomes, and epigenomes with the aim of discovering the molecular underpinnings of tumorigenesis, cancer progression, and therapy resistance. Multiple biological markers and pathways have been discovered to be tumor drivers, and a molecular classification of prostate cancer is emerging. Here, we highlight crucial findings of these genome-sequencing projects in localized and advanced disease. We recapitulate the utility and limitations of current clinical practices to diagnosis, prognosis, and therapy, and we provide examples of insights generated by the molecular profiling of tumors. Novel treatment concepts based on these molecular alterations are currently being addressed in clinical trials and will lead to an enhanced implementation of precision medicine strategies.

Genetics and biology of prostate cancer

Despite the high long-term survival in localized prostate cancer, metastatic prostate cancer remains largely incurable even after intensive multimodal therapy. The lethality of advanced disease is driven by the lack of therapeutic regimens capable of generating durable responses in the setting of extreme tumor heterogeneity on the genetic and cell biological levels. Here, we review available prostate cancer model systems, the prostate cancer genome atlas, cellular and functional heterogeneity in the tumor microenvironment, tumor-intrinsic and tumor-extrinsic mechanisms underlying therapeutic resistance, and technological advances focused on disease detection and management. These advances, along with an improved understanding of the adaptive responses to conventional cancer therapies, anti-androgen therapy, and immunotherapy, are catalyzing development of more effective therapeutic strategies for advanced disease. In particular, knowledge of the heterotypic interactions between and coevolution of cancer and host cells in the tumor microenvironment has illuminated novel therapeutic combinations with a strong potential for more durable therapeutic responses and eventual cures for advanced disease. Improved disease management will also benefit from artificial intelligence-based expert decision support systems for proper standard of care, prognostic determinant biomarkers to minimize overtreatment of localized disease, and new standards of care accelerated by next-generation adaptive clinical trials.

Peroxisomes and cancer: The role of a metabolic specialist in a disease of aberrant metabolism

Cancer is irrevocably linked to aberrant metabolic processes. While once considered a vestigial organelle, we now know that peroxisomes play a central role in the metabolism of reactive oxygen species, bile acids, ether phospholipids (e.g. plasmalogens), very-long chain, and branched-chain fatty acids. Immune system evasion is a hallmark of cancer, and peroxisomes have an emerging role in the regulation of cellular immune responses. Investigations of individual peroxisome proteins and metabolites support their pro-tumorigenic functions. However, a significant knowledge gap remains regarding how individual functions of proteins and metabolites of the peroxisome orchestrate its potential role as a pro-tumorigenic organelle. This review highlights new advances in our understanding of biogenesis, enzymatic functions, and autophagic degradation of peroxisomes (pexophagy), and provides evidence linking these activities to tumorigenesis. Finally, we propose avenues that may be exploited to target peroxisome-related processes as a mode of combatting cancer.

EMT, stemness and tumor plasticity in aggressive variant neuroendocrine prostate cancers

Neuroendocrine/Aggressive Variant Prostate Cancers are lethal variants of the disease, with an aggressive clinical course and very short responses to conventional therapy. The age-adjusted incidence rate for this tumor sub-type has steadily increased over the past 20 years in the United States, with no reduction in the associated mortality rate. The molecular networks fueling its emergence and sustenance are still obscure; however, many factors have been associated with the onset and progression of neuroendocrine differentiation in clinically typical adenocarcinomas including loss of androgen-receptor expression and/or signaling, conventional therapy, and dysregulated cytokine function. "Tumor-plasticity" and the ability to dedifferentiate into alternate cell lineages are central to this process. Epithelial-to-mesenchymal (EMT) signaling pathways are major promoters of stem-cell properties in prostate tumor cells. In this review, we examine the contributions of EMT-induced cellular-plasticity and stem-cell signaling pathways to the progression of Neuroendocrine/Aggressive Variant Prostate Cancers in the light of potential therapeutic opportunities.

Selective Actionable and Druggable Protein Kinases Drive the Progression of Neuroendocrine Prostate Cancer

Current clinical anti-androgen therapies in advanced prostate cancer (PCa) are driving an increased incidence of neuroendocrine prostate cancer (NEPC), a histological variant exhibiting reduced androgen receptor levels and expression of neuroendocrine markers. The mechanisms underlying the development of NEPC are poorly understood. A set of available data from a well-validated xenograft model of NEPC was used to analyze the exact role of protein kinase (PK) played in the development of NEPC. Fifty-four actionable and druggable PKs, mainly enriched in PI3K-Akt, mTOR, and MAPK signaling pathways, were screened out from the drastically changed PKs during NEPC transdifferentiation. Further analysis based on the crosstalk of these above signaling pathways finally singled out 10 PKs considered drivers and therapeutic targets in the development and treatment of NEPC. In vitro, the variation trend of PK expression observed during NEPC transdifferentiation could be recapitulated in PCa cell lines with different malignant degree. The predicted kinase targets exhibited different sensibilities in the restriction of PC3 cell growth. Selective actionable and druggable PKs may act as drivers in the progression of NEPC, and most of them can be used as potential therapeutic targets in clinical practice.

Roles of Alternative RNA Splicing of the Bif-1 Gene by SRRM4 During the Development of Treatment-induced Neuroendocrine Prostate Cancer

Treatment-induced neuroendocrine prostate cancer (t-NEPC) is an aggressive subtype of prostate cancer (PCa) that becomes more prevalent when hormonal therapy, chemotherapy, or radiation therapy is applied to patients with metastatic prostate adenocarcinoma (AdPC). How AdPC cells survive these anti-cancer therapies and progress into t-NEPC remains unclear. By comparing the whole transcriptomes between AdPC and t-NEPC, we identified Bif-1, an apoptosis-associated gene, which undergoes alternative RNA splicing in t-NEPC. We found that while Bif-1a is the predominant variant of the Bif-1 gene in AdPC, two neural-specific variants, Bif-1b and Bif-1c, are highly expressed in t-NEPC patients, patient derived xenografts, and cell models. The neural-specific RNA splicing factor, SRRM4, promotes Bif-1b and Bif-1c splicing, and the expression of SRRM4 in tumors is strongly associated with Bif-1b/-1c levels. Furthermore, we showed that Bif-1a is pro-apoptotic, while Bif-1b and Bif-1c are anti-apoptotic in PCa cells under camptothecin and UV light irritation treatments. Taken together, our data indicate that SRRM4 regulates alternative RNA splicing of the Bif-1 gene that enables PCa cells resistant to apoptotic stimuli under anti-cancer therapies, and may contribute to AdPC progression into t-NEPC.

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Alternative RNA splicing of the apoptosis-related gene, Bif-1, is associated with the development of t-NEPC.

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SRRM4 regulates alternative RNA splicing of the Bif-1 gene.

•

Bif-1a in AdPC cells is pro-apoptotic, while neural Bif-1 variants, Bif-1b/-1c, enable tumor cells resistant to apoptosis.

Treatment-induced neuroendocrine prostate cancer (t-NEPC) is an aggressive subtype of castration-resistant prostate cancer. It becomes more prevalent when more potent androgen receptor inhibitors are applied to patients. However, mechanisms by which t-NEPC develops remain unclear. Here we report alternative RNA splicing of the apoptosis-related gene, Bif-1, may contribute to t-NEPC establishment. We show that the expression of neural Bif-1 variants is upregulated in t-NEPC, and confers tumor cells resistance to apoptotic stimuli. We propose that tumor cells have to first develop mechanisms to counteract therapy-induced cell death before they can undergo neuroendocrine differentiation for t-NEPC.

Alternative RNA splicing of the MEAF6 gene facilitates neuroendocrine prostate cancer progression

Although potent androgen receptor pathway inhibitors (ARPI) improve overall survival of metastatic prostate cancer patients, treatment-induced neuroendocrine prostate cancer (t-NEPC) as a consequence of the selection pressures of ARPI is becoming a more common clinical issue. Improved understanding of the molecular biology of t-NEPC is essential for the development of new effective management approaches for t-NEPC. In this study, we identify a splice variant of the MYST/Esa1-associated factor 6 (MEAF6) gene, MEAF6-1, that is highly expressed in both t-NEPC tumor biopsies and neuroendocrine cell lines of prostate and lung cancers. We show that MEAF6-1 splicing is stimulated by neuronal RNA splicing factor SRRM4. Rather than inducing neuroendocrine trans-differentiation of cells in prostate adenocarcinoma, MEAF6-1 upregulation stimulates cell proliferation, anchorage-independent cell growth, invasion and xenograft tumor growth. Gene microarray identifies that these MEAF6-1 actions are in part mediated by the ID1 and ID3 genes. These findings suggest that the MEAF6-1 variant does not induce neuroendocrine differentiation of prostate cancer cells, but rather facilitates t-NEPC progression by increasing the proliferation rate of cells that have acquired neuroendocrine phenotypes.

Lineage Plasticity in Cancer Progression and Treatment

Historically, it has been widely presumed that differentiated cells are determined during development and become irreversibly committed to their designated fates. In certain circumstances, however, differentiated cells can display plasticity by changing their identity, either by dedifferentiation to a progenitor-like state or by transdifferentiation to an alternative differentiated cell type. Such cellular plasticity can be triggered by physiological or oncogenic stress, or it can be experimentally induced through cellular reprogramming. Notably, physiological stresses that promote plasticity, such as severe tissue damage, inflammation, or senescence, also represent hallmarks of cancer. Furthermore, key drivers of cellular plasticity include major oncogenic and tumor suppressor pathways and can be exacerbated by drug treatment. Thus, plasticity may help cancer cells evade detection and treatment. We propose that cancer can be considered as a disease of excess plasticity, a notion that has important implications for intervention and treatment.

Cellular plasticity and the neuroendocrine phenotype in prostate cancer

The success of next-generation androgen receptor (AR) pathway inhibitors, such as abiraterone acetate and enzalutamide, in treating prostate cancer has been hampered by the emergence of drug resistance. This acquired drug resistance is driven, in part, by the ability of prostate cancer cells to change their phenotype to adopt AR-independent pathways for growth and survival. Around one-quarter of resistant prostate tumours comprise cells that have undergone cellular reprogramming to become AR-independent and to acquire a continuum of neuroendocrine characteristics. These highly aggressive and lethal tumours, termed neuroendocrine prostate cancer (NEPC), exhibit reactivation of developmental programmes that are associated with epithelial-mesenchymal plasticity and acquisition of stem-like cell properties. In the past few years, our understanding of the link between lineage plasticity and an emergent NEPC phenotype has considerably increased. This new knowledge can contribute to novel therapeutic modalities that are likely to improve the treatment and clinical management of aggressive prostate cancer.

Clinical and molecular features of treatment-related neuroendocrine prostate cancer

Treatment-related neuroendocrine prostate cancer is a lethal form of prostate cancer that emerges in the later stages of castration-resistant prostate cancer treatment. Treatment-related neuroendocrine prostate cancer transdifferentiates from adenocarcinoma as an adaptive response to androgen receptor pathway inhibition. The incidence of treatment-related neuroendocrine prostate cancer has been rising due to the increasing use of potent androgen receptor pathway inhibitors. Typically, treatment-related neuroendocrine prostate cancer is characterized by either low or absent androgen receptor expression, small cell carcinoma morphology and expression of neuroendocrine markers. Clinically, it manifests with predominantly visceral or lytic bone metastases, bulky tumor masses, low prostate-specific antigen levels or a short response duration to androgen deprivation therapy. Furthermore, although the tumor initially responds to platinum-based chemotherapy, the duration of the response is short. Based on the poor prognosis, it is imperative to identify novel molecular targets for treatment-related neuroendocrine prostate cancer. Recent advances in genomic and molecular research, supported by novel in vivo models, have identified some of the key molecular characteristics of treatment-related neuroendocrine prostate cancer. The gain of MYCN and AURKA oncogenes, along with the loss of tumor suppressor genes TP53 and RB1 are key genomic alterations associated with treatment-related neuroendocrine prostate cancer. Androgen receptor repressed genes, such as BRN2 and PEG10, are also necessary for treatment-related neuroendocrine prostate cancer. These genetic changes converge on pathways upregulating genes, such as SOX2 and EZH2, that facilitate lineage plasticity and neuroendocrine differentiation. As a result, on potent androgen receptor pathway inhibition, castration-resistant prostate cancer transdifferentiates to treatment-related neuroendocrine prostate cancer in a clonally divergent manner. Further understanding of the disease biology is required to develop novel drugs and biomarkers that would help treat this aggressive prostate cancer variant.

Neuroendocrine tumors of the prostate

Neuroendocrine (NE) differentiation in tumors of the prostate or in the setting of prostate cancer (PCa) is rare. A survey of these lesions is presented, including usual PCa with focal NE marker-positive cells, Paneth cell-like change, prostatic 'carcinoid', high-grade NE carcinoma, as well as other tumors that do not fit neatly into these categories. The most significant clinical and pathologic features, emerging molecular evidence and the importance of differentiating NE tumors involving the prostate from secondary involvement are highlighted.

TMPRSS2-ERG fusions unexpectedly identified in men initially diagnosed with nonprostatic malignancies

Background

TMPRSS2-ERG gene fusions are frequently found in prostate cancer and are pathognomomic for prostatic origin. In a series of cancer cases assayed with comprehensive genomic profiling (CGP) in the course of clinical care, we reviewed the frequency of TMPRSS2-ERG fusions in patient tumors of various histologic subtypes.

Methods

Frequency of TMPRSS2-ERG fusions was determined in comprehensive genomic profiles from 64,263 cancer cases submitted to Foundation Medicine to assess genomic alterations suggesting benefit from targeted therapy. Genomic results from an index case of prostate cancer that underwent evolution from adenocarcinoma to pure squamous cell carcinoma are presented.

Results

TMPRSS2-ERG fusions were identified for 0.86% (250/29030) of male patients and not found for female patients (0/35233). TMPRSS2-ERG fusions were detected in six tumors that were classified as squamous carcinoma, five of which were of unknown primary site. The index case is a patient with a large left retrovesical mass diagnosed as squamous carcinoma by morphologic examination and a history of Gleason 9 prostate cancer with prior prostatectomy and salvage radiation therapy. TMPRSS2-ERG was detected by genomic profiling in the squamous cell tumor, the primary adenocarcinoma of the prostate, and in a metachronous prostatic adenocarcinoma metastasis. Based on these results, the patient received androgen deprivation therapy. A phylogenetic tree demonstrating clonal and histopathologic evolution of prostate cancer in the index patient was constructed.

Conclusions

In this large CGP dataset, TMPRSS2-ERG fusion was seen in ~30% of prostate cancers regardless of histologic type; the fusion was on occasion detected in advanced cancers not initially carrying a diagnosis of prostate carcinoma. CGP of advanced cancers in men may reveal prostatic origin by detection of the pathognomomic TMPRSS2-ERG fusion gene.

Establishment of a neuroendocrine prostate cancer model driven by the RNA splicing factor SRRM4

Neuroendocrine prostate cancer (NEPC) is becoming more prevalent as more potent androgen receptor (AR) pathway inhibitors are applied to patients with metastatic tumors. However, there are limited cell and xenograft models currently available, hindering the investigation of signal pathways involved in regulating NEPC progression and the design of high throughput screening assays for inhibitors to treat NEPC patients. Here, we report an NEPC model, LnNE, that is derived from prostate adenocarcinoma cells and has global similarity in transcription and RNA splicing to tumors from NEPC patients. LnNE xenografts are castrate-resistant and highly aggressive. Its tumor take is ∼3-5 weeks and tumor doubling time is ∼2-3 weeks. LnNE expresses multiple neuroendocrine markers, preserves AR expression, but is PSA negative. Its neuroendocrine phenotype cannot be reversed by androgen treatment. LnNE cells grow as multi-cellular spheroids under 2-dimensional culture conditions similar to the NEPC cell line NCI-H660, but have higher proliferation rate and are easier to be transfected. LnNE cells can also adapt to 3-dimensional culture conditions in a 96-plate format, allowing high throughput screening assays. In summary, the LnNE model is useful to study the mechanisms of NEPC progression and to discover potential therapies for NEPC.

Correlation between ERG Fusion Protein and Androgen Receptor Expression by Immunohistochemistry in Prostate, Possible Role in Diagnosis and Therapy

Background: Recent discovery of gene rearrangements have brought a new look to the molecular pathogenesis of cancer. Gene fusions occur in nearly 60% of prostate adenocarcinoma, being the TMPRSS2-ERG one of the most common. Evidence supports the role of ERG fusion in tumorigenesis, progression and invasion via effecting pathways such as WNT, MYC, uPA, PI3K/AKT/PTEN, RAS/RAF/MAPF, NKX3.1, GST-pi and androgen receptor (AR) mediated signaling. Most of the ERG fusions involve 5'-partners androgen responsive. Therefore, we aimed to evaluate AR and ERG fusion protein expression on prostate tissue to find clinicopathological applications and possible role in therapy.

Methods: One hundred three samples, including prostate core biopsies and radical prostatectomy specimens, were evaluated for ERG and AR expression by immunohistochemistry (IHC). ERG rearrangement was done by fluorescence in situ hybridization (FISH) on 11 randomly selected cases and correlated with IHC results.

Results: From the total of 103 samples, eight (8/103) were benign, fourteen (14/103) had atypical glands, two (2/103) had prostatic intraepithelial neoplasia (PIN), and seventy nine (79/103) showed prostate adenocarcinoma. Forty four (44/79) tumor cases were Gleason score (GS) 6-7 (lower GS), and thirty five (35/79) were GS of 8-10 (higher GS). ERG immunoreaction was observed in 27.8% (22/79) of the tumor cases, showing higher expression in those with lower GS (68.2%, 15/22) compared to higher GS (31.8%, 7/22). Neither benign glands nor PIN stained with ERG. AR expression was observed in 75% of benign samples, 78.5% of atypical glands, 100% of PIN, and in 87.3% of tumor cases with no significant difference based on GS. Co-expression of ERG and AR was evaluated on all the tumor samples. ERG+/AR+ was seen in 77.3% (17/22) of the ERG+ tumor cases, with higher frequency in lower GS (64.7%, 11/17) compared to those with higher GS (35.3%, 6/17). All but five corresponding ERG+ tumor samples were negative for AR. Only 5 samples were ERG-/AR- corresponding to adenocarcinoma GS of 6. Presence or absence of ERG rearrangement was confirmed by FISH and correlated with IHC results.

Conclusions: Characterization of ERG status by IHC in prostate tissue has an excellent correlation with FISH. It may also assist in diagnosis since none of the benign glands stained with ERG. Co-expression of ERG+/AR+ in prostate tumor by IHC may suggest gene fusion between ERG and a 5'-partner driven by androgen signaling such as TMPRSS2, which it could represent an important ancillary test for clinical management and development of new therapeutic targets.

Severe Cushing's syndrome due to small cell prostate carcinoma: a case and review of literature

Cushing's syndrome (CS) due to ectopic adrenocorticotrophic hormone (ACTH) is associated with a variety of tumours most of which arise in the thorax or abdomen. Prostate carcinoma is a rare but important cause of rapidly progressive CS. To report a case of severe CS due to ACTH production from prostate neuroendocrine carcinoma and summarise previous published cases. A 71-year-old male presented with profound hypokalaemia, oedema and new onset hypertension. The patient reported two weeks of weight gain, muscle weakness, labile mood and insomnia. CS due to ectopic ACTH production was confirmed with failure to suppress cortisol levels following low- and high-dose dexamethasone suppression tests in the presence of a markedly elevated ACTH and a normal pituitary MRI. Computed tomography demonstrated an enlarged prostate with features of malignancy, confirmed by MRI. Subsequent prostatic biopsy confirmed neuroendocrine carcinoma of small cell type and conventional adenocarcinoma of the prostate. Adrenal steroidogenesis blockade was commenced using ketoconazole and metyrapone. Complete biochemical control of CS and evidence of disease regression on imaging occurred after four cycles of chemotherapy with carboplatin and etoposide. By the sixth cycle, the patient demonstrated radiological progression followed by recurrence of CS and died nine months after initial presentation. Prostate neuroendocrine carcinoma is a rare cause of CS that can be rapidly fatal, and early aggressive treatment of the CS is important. In CS where the cause of EAS is unable to be identified, a pelvic source should be considered and imaging of the pelvis carefully reviewed.

Transdifferentiation as a Mechanism of Treatment Resistance in a Mouse Model of Castration-Resistant Prostate Cancer

Current treatments for castration-resistant prostate cancer (CRPC) that target androgen receptor (AR) signaling improve patient survival, yet ultimately fail. Here, we provide novel insights into treatment response for the antiandrogen abiraterone by analyses of a genetically engineered mouse (GEM) model with combined inactivation of Trp53 and Pten, which are frequently comutated in human CRPC. These NPp53 mice fail to respond to abiraterone and display accelerated progression to tumors resembling treatment-related CRPC with neuroendocrine differentiation (CRPC-NE) in humans. Cross-species computational analyses identify master regulators of adverse response that are conserved with human CRPC-NE, including the neural differentiation factor SOX11, which promotes neuroendocrine differentiation in cells derived from NPp53 tumors. Furthermore, abiraterone-treated NPp53 prostate tumors contain regions of focal and/or overt neuroendocrine differentiation, distinguished by their proliferative potential. Notably, lineage tracing in vivo provides definitive and quantitative evidence that focal and overt neuroendocrine regions arise by transdifferentiation of luminal adenocarcinoma cells. These findings underscore principal roles for TP53 and PTEN inactivation in abiraterone resistance and progression from adenocarcinoma to CRPC-NE by transdifferentiation.Significance: Understanding adverse treatment response and identifying patients likely to fail treatment represent fundamental clinical challenges. By integrating analyses of GEM models and human clinical data, we provide direct genetic evidence for transdifferentiation as a mechanism of drug resistance as well as for stratifying patients for treatment with antiandrogens. Cancer Discov; 7(7); 736-49. ©2017 AACR.See related commentary by Sinha and Nelson, p. 673This article is highlighted in the In This Issue feature, p. 653.

[Neuroendocrine prostate cancer: Natural history, molecular features, therapeutic management and future directions]

Neuroendocrine prostate cancer is a rare malignancy with a an adverse prognostic. Histologically, It can be pure (small cells or large cells neuroendocrine carcinoma) or mixed with a adenocarcinoma component. Rarely diagnosed de novo, neuroendocrine prostate cancer is generally associated with advanced stage disease resistant to castration. As such, this histological subtype could represent an aggressive evolution of prostatic adenocarcinoma, through the epithelio-neuroendocrine transdifferentiation mechanism (phenomenon of lineage plasticity). Nonetheless, neuroendocrine prostate cancer is a heterogeneous malignancy with multiple histopathological variants showing distinct clinical features. The broad variety of molecular analyses could help to understand the ontogeny of this histological subtype and its signaling pathways. This may also allow identifying diagnostic and prognostic biomarkers as well as potential molecular targets. However, treatment options are currently limited and consist only in platinium-based chemotherapy for advanced stage disease.

Emerging Variants of Castration-Resistant Prostate Cancer

Metastatic castration-resistant prostate cancer (CRPC) is associated with substantial clinical, pathologic, and molecular heterogeneity. Most tumors remain driven by androgen receptor (AR) signaling, which has clinical implications for patient selection for AR-directed approaches. However, histologic and clinical resistance phenotypes can emerge after AR inhibition, in which the tumors become less dependent on the AR. In this review, we discuss prostate cancer variants including neuroendocrine (NEPC) and aggressive variant (AVPC) prostate cancers and their clinical implications. Improvements in the understanding of the biologic mechanisms and molecular features underlying prostate cancer variants may help prognostication and facilitate the development of novel therapeutic approaches for subclasses of patient with CRPC.

Strategies to avoid treatment-induced lineage crisis in advanced prostate cancer

The increasing potency of therapies that target the androgen receptor (AR) signalling axis has correlated with a rise in the proportion of patients with prostate cancer harbouring an adaptive phenotype, termed treatment-induced lineage crisis. This phenotype is characterized by features that include soft-tissue metastasis and/or resistance to standard anticancer therapies. Potent anticancer treatments might force cancer cells to evolve and develop alternative cell lineages that are resistant to primary therapies, a mechanism similar to the generation of multidrug- resistant microorganisms after continued antibiotic use. Herein, we assess the hypothesis that treatment-adapted phenotypes harbour reduced AR expression and/or activity, and acquire compensatory strategies for cell survival. We highlight the striking similarities between castration-resistant prostate cancer and triple-negative breast cancer, another poorly differentiated endocrine malignancy. Alternative treatment paradigms are needed to avoid therapy-induced resistance. Herein, we present a new clinical trial strategy designed to evaluate the potential of rapid drug cycling as an approach to delay the onset of resistance and treatment-induced lineage crisis in patients with metastatic castration-resistant prostate cancer.

Rb1 and Trp53 cooperate to suppress prostate cancer lineage plasticity, metastasis, and antiandrogen resistance

Prostate cancer relapsing from antiandrogen therapies can exhibit variant histology with altered lineage marker expression, suggesting that lineage plasticity facilitates therapeutic resistance. The mechanisms underlying prostate cancer lineage plasticity are incompletely understood. Studying mouse models, we demonstrate that Rb1 loss facilitates lineage plasticity and metastasis of prostate adenocarcinoma initiated by Pten mutation. Additional loss of Trp53 causes resistance to antiandrogen therapy. Gene expression profiling indicates that mouse tumors resemble human prostate cancer neuroendocrine variants; both mouse and human tumors exhibit increased expression of epigenetic reprogramming factors such as Ezh2 and Sox2. Clinically relevant Ezh2 inhibitors restore androgen receptor expression and sensitivity to antiandrogen therapy. These findings uncover genetic mutations that enable prostate cancer progression; identify mouse models for studying prostate cancer lineage plasticity; and suggest an epigenetic approach for extending clinical responses to antiandrogen therapy.

New and Emerging Diagnostic and Prognostic Immunohistochemical Biomarkers in Prostate Pathology

The diagnosis of minimal prostatic adenocarcinoma can be challenging on prostate needle biopsy, and immunohistochemistry may be used to support the diagnosis of cancer. The International Society of Urologic Pathology currently recommends the use of the basal cell markers high-molecular-weight cytokeraratin and p63, and α-methylacyl-coenzyme-A racemase. However, there are caveats associated with the interpretation of these markers, particularly with benign mimickers. Another issue is that of early detection of presence and progression of disease and prediction of recurrence after clinical intervention. There remains a lack of reliable biomarkers to accurately predict low-risk cancer and avoid over treatment. As such, aggressive forms of prostate cancer may be missed and indolent disease may be subjected to unnecessary radical therapy. New biomarker discovery promises to improve early detection and prognosis and to provide targets for therapeutic interventions. In this review, we present the emerging immunohistochemical biomarkers of prostate cancer PTEN, ERG, FASN, MAGI-2, and SPINK1, and address their diagnostic and prognostic advantages and limitations.

N-Myc Induces an EZH2-Mediated Transcriptional Program Driving Neuroendocrine Prostate Cancer

The transition from castration-resistant prostate adenocarcinoma (CRPC) to neuroendocrine prostate cancer (NEPC) has emerged as an important mechanism of treatment resistance. NEPC is associated with overexpression and gene amplification of MYCN (encoding N-Myc). N-Myc is an established oncogene in several rare pediatric tumors, but its role in prostate cancer progression is not well established. Integrating a genetically engineered mouse model and human prostate cancer transcriptome data, we show that N-Myc overexpression leads to the development of poorly differentiated, invasive prostate cancer that is molecularly similar to human NEPC. This includes an abrogation of androgen receptor signaling and induction of Polycomb Repressive Complex 2 signaling. Altogether, our data establishes N-Myc as an oncogenic driver of NEPC.

ERG expression in prostate cancer: biological relevance and clinical implication

INTRODUCTION

Screening for increased levels of prostate-specific antigen (PSA) has allowed early detection of a large majority of prostate cancer (PCa) cases. However, the relative lack of specificity of PSA has resulted in significant over-diagnosis and unnecessary treatment for indolent tumors. The fusion of the transmembrane protease serine 2 with E26 transformation-specific family genes, particularly ERG, is the most widespread genetic alteration in prostate cancer, and data suggest that it is more specific for neoplastic prostate disease and may be of added prognostic value and point toward molecular subtype of PCa.

METHODS

In this review, retrospective studies and clinical trials were analyzed to highlight the recent advances in our understanding of the cellular consequence of ERG rearrangement, describe its interactions with other genetic and molecular pathways, and discuss its potential diagnostic and prognostic value.

CONCLUSION

ERG over-expression has an emerging role in the diagnosis of PCa pathology, although there is still debate about its prognostic value. Elucidation of the mechanisms of ERG gene rearrangements and expression promises novel therapeutic and diagnostic avenues for prostate cancer.

Genomic predictors for treatment of late stage prostate cancer

In spite of the development of new treatments for late stage prostate cancer, significant challenges persist to match individuals with effective targeted therapies. Genomic classification using high-throughput sequencing technologies has the potential to achieve this goal and make precision medicine a reality in the management of men with castrate-resistant prostate cancer. This chapter reviews some of the most recent studies that have resulted in significant progress in determining the landscape of somatic genomic alterations in this cohort and, more importantly, have provided clinically actionable information that could guide treatment decisions. This chapter reviews the current understanding of common alterations such as alterations of the androgen receptor and PTEN pathway, as well as ETS gene fusions and the growing importance of PARP inhibition. It also reviews recent studies that characterize the evolution to neuroendocrine tumors, which is becoming an increasingly important clinical problem. Finally, this chapter reviews recent innovative studies that characterize the compelling evolutionary history of lethal prostate cancer evidenced by polyclonal seeding and interclonal cooperation between metastasis and the importance of tumor clone dynamics measured serially in response to treatment. The genomic landscape of late stage prostate cancer is becoming better defined, and the prospect for assigning clinically actionable data to inform rationale treatment for individuals with this disease is becoming a reality.

High alpha-methylacyl-CoA racemase (AMACR) is associated with ERG expression and with adverse clinical outcome in patients with localized prostate cancer

Alpha-methylacyl-CoA racemase (AMACR) is a well-characterized marker extensively utilized in prostate cancer (PCA) diagnosis. However, the prognostic value of AMACR expression and its relation to TMPRSS2-ERG gene rearrangement as one of the most common molecular alterations in PCA is not fully explored. AMACR expression was investigated in a cohort of 218 men with localized PCA treated by radical prostatectomy and correlated with ERG and various clinical and pathological parameters. In vitro studies assessed AMACR changes to ERG knockdown and other related genes. In addition, bioinformatics validated the significance of AMACR/ERG expression and assessed relevant genetic signatures in relation to AMACR/ERG expression. AMACR expression was significantly associated with disease progression and with ERG (p ∼0). Seventeen percent of cancer foci showed negative/weak AMACR expression while being ERG positive. High AMACR expression was significantly associated with positive surgical margins (p = 0.01), specifically in tumors with lower Gleason score <7, with ∼95 % exhibiting positive surgical margin (p = 0.008). High AMACR showed marginal association with PSA biochemical recurrence (BCR) (p = 0.06) which was slightly more pronounced in ERG-positive tumors (p = 0.04). This was validated in other public cohorts. However, in this cohort, the association with BCR was not statistically significant in multivariate analysis (p = 0.09). Using in vitro cellular models, AMACR messenger RNA (mRNA) expression, but not protein levels, showed an association with ERG expression. We report for the first time a significant association between AMACR and ERG with prognostic implication. Patients with high AMACR/ERG-positive PCA may be at higher risk for disease progression, and additional studies in larger cohorts are needed to confirm the above findings. Functional studies investigating the molecular pathways connecting AMACR and ERG may provide an additional insight into PCA progression pathways.

Small cell carcinoma of the urinary bladder: changing trends in the current literature

Background Extrapulmonary small cell carcinoma (SmCC), also known as oat cell carcinoma or small cell neuroendocrine carcinoma, is characterized by an aggressive clinical course with early metastasis pattern and a short life expectancy. So far, there is no prospective, data-based case-control study due to its low incidence. The purpose of this paper is to discuss the epidemiology, morphopathology, clinical characteristics, differential diagnosis and treatment of bladder SmCC in the light of the literature. Scope PubMed and American Society of Clinical Oncology Meeting abstracts were searched according to the following keywords: 'extrapulmonary SmCC', 'bladder cancer', and 'therapeutic approach'. The last search was performed on 1 October 2015. Some additional papers were determined by reviewing references of the appropriate articles. Most of the data regarding small cell carcinoma of the urinary bladder (SmCCB) were found to be based on the retrospective trials. Findings Bladder SmCC is more frequent in men and usually appears in the seventh to eighth decades. Macroscopic hematuria is the most common clinical symptom. The diagnosis of SmCCB is performed based on the same criteria determined by the WHO classification for the diagnosis of small cell lung carcinoma (SCLC). Prognosis is closely correlated with the stage at presentation. Although the prognosis of the disease is poor, a long survival can be achieved particularly by radical surgery following neoadjuvant chemotherapy in patients with early stage tumors. Cystectomy is still the current standard local treatment. However, cystectomy alone is not sufficient. Chemotherapy and definitive radiotherapy should be preferred for limited disease in patients who are not candidate for surgery. Conclusion Considering the poor prognosis of the disease, further studies are needed to determine the optimal treatment options and new molecular markers in the way of early diagnosis and favorable outcomes. Prospective, multicenter, randomized studies are required to evaluate the role of neoadjuvant chemotherapy followed either by surgery or radiotherapy.

Neuroendocrine Tumors of the Prostate: Emerging Insights from Molecular Data and Updates to the 2016 World Health Organization Classification

Neuroendocrine neoplasms of the prostate represent a multifarious group of tumors that exist both in pure forms and associated with prostatic adenocarcinoma. Morphologically, neuroendocrine cells in prostate neoplasms can range from being indistinguishable from surrounding prostate adenocarcinoma cells to having high-grade neuroendocrine appearances similar to neuroendocrine malignancies of other organs. On the molecular level, neuroendocrine malignancies arising in the setting of prostate adenocarcinoma have been the subject of a large amount of recent research, most of which has supported the conclusion that neuroendocrine malignancy within the prostate develops as a transdifferentiation from prostate adenocarcinoma. There has not, however, been substantial investigation into rare, pure neuroendocrine malignancies and the possibility that these tumors may have a different cell of origin and molecular genesis. Here, we discuss the morphologic spectrum of malignant neuroendocrine prostate neoplasms and review the most recent molecular data on the subject of malignant neuroendocrine differentiation in prostatic adenocarcinoma. In reflection of the most recent data, we also discuss diagnostic classification of prostate neuroendocrine tumors with reference to the 2016 World Health Organization (WHO) classification. We discuss the reporting of these tumors, placing emphasis on the differentiation between pure and mixed neuroendocrine malignancies so that, in the least, they can be easily identified for the purposes of future clinical and laboratory-based investigation. Finally, we suggest a designation for an unclassifiable (or not otherwise specified) high-grade neuroendocrine prostate malignancy whose features do not easily place it into one of the WHO diagnostic entities.

ERG and PTEN status of isolated high-grade PIN occurring in cystoprostatectomy specimens without invasive prostatic adenocarcinoma

High-grade prostatic intraepithelial neoplasia (HGPIN) is widely believed to represent a precursor to invasive prostatic adenocarcinoma. However, recent molecular studies have suggested that retrograde spread of invasive adenocarcinoma into pre-existing prostatic ducts can morphologically mimic HGPIN. Thus, previous molecular studies characterizing morphologically identified HGPIN occurring in radical prostatectomies or needle biopsies with concurrent invasive carcinoma may be partially confounded by intraductal spread of invasive tumor. To assess ERG and PTEN status in HGPIN foci likely to represent true precursor lesions in the prostate, we studied isolated HGPIN occurring without associated invasive adenocarcinoma in cystoprostatectomies performed at Johns Hopkins between 2009 and 2014. Of 344 cystoprostatectomies, 33% (115/344) contained invasive prostatic adenocarcinoma in the partially submitted prostate (10 blocks/case on average) and were excluded from the study. Of the remaining cases without sampled cancer, 32% (73/229) showed 133 separate foci of HGPIN and were immunostained for ERG and PTEN using genetically validated protocols. Of foci of HGPIN with evaluable staining, 7% (8/107) were positive for ERG. PTEN loss was not seen in any HGPIN lesion (0/88). Because these isolated HGPIN foci at cystoprostatectomy are unlikely to represent retrograde spread of invasive tumor, our study suggests that ERG rearrangement, but not PTEN loss, is present in a minority of potential neoplastic precursor lesions in the prostate.

SRRM4 Drives Neuroendocrine Transdifferentiation of Prostate Adenocarcinoma Under Androgen Receptor Pathway Inhibition

BACKGROUND

Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of castration-resistant prostate cancer that typically does not respond to androgen receptor pathway inhibition (ARPI), and its diagnosis is increasing.

OBJECTIVE

To understand how NEPC develops and to identify driver genes to inform therapy for NEPC prevention.

DESIGN, SETTING, AND PARTICIPANTS

Whole-transcriptome sequencing data were extracted from prostate tumors from two independent cohorts: The Beltran cohort contained 27 adenocarcinoma and five NEPC patient samples, and the Vancouver Prostate Centre cohort contained three patient samples and nine patient-derived xenografts.

INTERVENTION

A novel bioinformatics tool, comparative alternative splicing detection (COMPAS), was invented to analyze alternative RNA splicing on RNA-sequencing data.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

COMPAS identified potential driver genes for NEPC development. Biochemical and biological validations were performed in both prostate cell and tumor models.

RESULTS AND LIMITATION

More than 66% of the splice events were predicted to be regulated by the RNA splicing factor serine/arginine repetitive matrix 4 (SRRM4). In vitro and in vivo evidence confirmed that one SRRM4 target gene was the RE1 silencing transcription factor (REST), a master regulator of neurogenesis. Moreover, SRRM4 strongly stimulated adenocarcinoma cells to express NEPC biomarkers, and this effect was exacerbated by ARPI. ARPI combined with a gain of SRRM4-induced adenocarcinoma cells to assume multicellular spheroid morphology and was essential in establishing progressive NEPC xenografts. These SRRM4 actions were further enhanced by loss of function of TP53.

CONCLUSIONS

SRRM4 drives NEPC progression. This knowledge may guide the development of novel therapeutics aimed at NEPC.

PATIENT SUMMARY

Using next-generation RNA sequencing and our newly developed bioinformatics tool, we identified a neuroendocrine prostate cancer (NEPC)-specific RNA splicing signature that is predominantly controlled by serine/arginine repetitive matrix 4 (SRRM4). We confirmed that SRRM4 drives NEPC progression, and we propose SRRM4 as a potential therapeutic target for NEPC.