Estrogen receptor beta expression in triple negative breast cancers is not associated with recurrence or survival.

BACKGROUND: Triple negative BCa (TNBC) is defined by a lack of expression of estrogen (ERα), progesterone (PgR) receptors and human epidermal growth factor receptor 2 (HER2) as assessed by protein expression and/or gene amplification. It makes up ~ 15% of all BCa and often has a poor prognosis. TNBC is not treated with endocrine therapies as ERα and PR negative tumors in general do not show benefit. However, a small fraction of the true TNBC tumors do show tamoxifen sensitivity, with those expressing the most common isoform of ERß1 having the most benefit. Recently, the antibodies commonly used to assess ERß1 in TNBC have been found to lack specificity, which calls into question available data regarding the proportion of TNBC that express ERß1 and any relationship to clinical outcome. METHODS: To confirm the true frequency of ERß1 in TNBC we performed robust ERß1 immunohistochemistry using the specific antibody CWK-F12 ERß1 on 156 primary TNBC cancers from patients with a median of 78 months (range 0.2-155 months) follow up. RESULTS: We found that high expression of ERß1 was not associated with increased recurrence or survival when assessed as percentage of ERß1 positive tumor cells or as Allred > 5. In contrast, the non-specific PPG5-10 antibody did show an association with recurrence and survival. CONCLUSIONS: Our data indicate that ERß1 expression in TNBC tumours does not associate with prognosis.

LOT and HOT or not. The proliferation of clinically insignificant and poorly characterised types of renal neoplasia.

The classification of malignant tumours is influenced by both immunohistochemical and molecular genetic findings. This is highlighted in the latest World Health Organization classification of renal neoplasia, which has a tumour category of 'tumours that are molecularly defined'. This implies that the defining molecular features are integral to tumourigenesis, which may not necessarily be the case. Renal oncocytoma is recognised as a benign tumour with variable morphology and immunoexpression. A variant of these tumours is hybrid oncocytic chromophobe tumour, which has features of both oncocytoma and chromophobe renal cell carcinoma and may, on rare occasions, show malignant behaviour. Recent reports have proposed two further entities with eosinophilic cytoplasm and varying nuclear pleomorphism, designated low grade oncocytic tumour (LOT) and eosinophilic vacuolated tumour (EVT), formally known as high grade oncocytic tumour (HOT). The diagnosis of these apparently benign tumours was made on the basis of morphological and immunohistochemical features. More recently it has been claimed that the mutations in the mTOR pathway are also a diagnostic feature and it is further suggested that these mutations are key to the pathogenesis of these tumours. As is seen in oncocytoma, immunohistochemical expression of tumours included in series of LOT and EVT is variable. The mutations in the mTOR pathway, where detected, were not constant, with any combination of mTOR, TSC1 and/or TSC2 being involved. A major issue is that in many of the studies full comparative genomic hybridisation results are not presented. In addition it is well recognised that mTOR mutations are seen in a variety of renal tumours. In view of these conflicting results, the rarity of these tumours and their apparent benign nature, raises questions as to why these tumours should be considered specific entities.

Cribriform pattern disease over-represented in pelvic lymph node metastases identified on 68GA PSMA-PET/CT.

Objectives: To determine whether any specific histologic subtype of prostate cancer was preferentially represented in pelvic lymph node metastases identified on 68GA-PSMA-PET/CT. Subjects and Methods: A consecutive series of 66 men with biochemical recurrent prostate cancer was evaluated with 68GA-PSMA-PET/CT. Where disease was confined to pelvic lymph nodes, patients were offered salvage extended pelvic lymph node dissection. Twenty patients ultimately proceeded to extended bilateral template pelvic lymph node dissection. Lymph node positivity and the histologic subtype of apparent cancer were assessed, as was PSA response to this intervention. Results: Mean PSA at time of PSMA scanning for patients undergoing lymphadenectomy was 2.49 (n = 20, range 0.21-12.0). In 16 of 20 patients, there was evidence of metastatic cribriform pattern prostate cancer in excised nodes (100% cribriform pattern in 11/16). Only four of 20 patients had no evidence of this histologic subtype of disease. PSA response was not related to the presence or proportional amount of cribriform pattern disease identified. Conclusions: Cribriform pattern adenocarcinoma appears to be the histologic subtype preferentially identified in pelvic lymph nodes on 68GA-PSMA-PET/CT. The use of PSMA-PET may be particularly valuable in staging of primary or biochemically recurrent prostate cancer in patients with cribriform pattern disease detected on initial biopsy or radical prostatectomy. Further research is required to further confirm the observed association.

Novel Germline Mutations in a Cohort of Men with Familial Prostate Cancer.

Background: Germline mutations in BRCA2 are associated with aggressive prostate cancer. Additional information regarding the clinical phenotype of germline pathogenic variants in other prostate cancer predisposition genes is required. Clinical testing has been limited by evidence, further restricting knowledge of variants that contribute to prostate cancer development. Objective: Prostate cancer patients who were first- and second-degree relatives from multi-case prostate cancer families underwent a gene panel screen to identify novel (non-BRCA) germline pathogenic variants in cancer predisposition genes and define clinical phenotypes associated with each gene. Methods: The germline genomic DNA (gDNA) of 94 index cases with verified prostate cancer from families with a minimum of two verified prostate cancer cases was screened with an 84-cancer-gene panel. Families were recruited for multi-case breast/ovarian cancer (n = 66), or multi-case prostate cancer (n = 28). Prostate cancer characteristics associated with each gene were compared with prostate cancer cases of confirmed non-mutation carriers (BRCAX), also from multi-case prostate cancer families (n = 111), and with data from the Prostate Cancer Outcomes Registry (PCOR). Results: Ninety-four prostate cancer index cases underwent gene panel testing; twenty-two index cases (22/94; 23%) were found to carry a class 4-5 (C4/5) variant. Six of twenty-two (27%) variants were not clinically notifiable, and seven of twenty-two (31.8%) variants were in BRCA1/2 genes. Nine of twenty-two (40.9%) index cases had variants identified in ATM (n = 4), CHEK2 (n = 2) and HOXB13G84 (n = 3); gDNA for all relatives of these nine cases was screened for the corresponding familial variant. The final cohort comprised 15 confirmed germline mutation carriers with prostate cancer (ATM n = 9, CHEK2 n = 2, HOXB13G84 n = 4). ATM and CHEK2-associated cancers were D'Amico intermediate or high risk, comparable to our previously published BRCA2 and BRCAX prostate cancer cohort. HOXB13G84 carriers demonstrated low- to intermediate-risk prostate cancer. In the BRCAX cohort, 53.2% of subjects demonstrated high-risk disease compared with 25% of the PCOR cohort. Conclusions:ATM and CHEK2 germline mutation carriers and the BRCAX (confirmed non-mutation carriers) cohort demonstrated high risk disease compared with the general population. Targeted genetic testing will help identify men at greater risk of prostate-cancer-specific mortality. Data correlating rare variants with clinical phenotype and familial predisposition will strengthen the clinical validity and utility of these results and establish these variants as significant in prostate cancer detection and management.

Tumor immune microenvironment of primary prostate cancer with and without germline mutations in homologous recombination repair genes.

BACKGROUND: Aberrations in homologous recombination repair (HRR) genes are emerging as important biomarkers for personalized treatment in prostate cancer (PCa). HRR deficiency (HRD) could affect the tumor immune microenvironment (TIME), potentially contributing to differential responses to poly ADP-ribose polymerase (PARP) inhibitors and immune checkpoint inhibitors. Spatial distribution of immune cells in a range of cancers identifies novel disease subtypes and is related to prognosis. In this study we aimed to determine the differences in the TIME of PCa with and without germline (g) HRR mutations. METHODS: We performed gene expression analysis, multiplex immunohistochemistry of T and B cells and quantitative spatial analysis of PCa samples from 36 patients with gHRD and 26 patients with sporadic PCa. Samples were archival tumor tissue from radical prostatectomies with the exception of one biopsy. Results were validated in several independent cohorts. RESULTS: Although the composition of the T cell and B cells was similar in the tumor areas of gHRD-mutated and sporadic tumors, the spatial profiles differed between these cohorts. We describe two T-cell spatial profiles across primary PCa, a clustered immune spatial (CIS) profile characterized by dense clusters of CD4+ T cells closely interacting with PD-L1+ cells, and a free immune spatial (FIS) profile of CD8+ cells in close proximity to tumor cells. gHRD tumors had a more T-cell inflamed microenvironment than sporadic tumors. The CIS profile was mainly observed in sporadic tumors, whereas a FIS profile was enriched in gHRD tumors. A FIS profile was associated with lower Gleason scores, smaller tumors and longer time to biochemical recurrence and metastasis. CONCLUSIONS: gHRD-mutated tumors have a distinct immune microenvironment compared with sporadic tumors. Spatial profiling of T-cells provides additional information beyond T-cell density and is associated with time to biochemical recurrence, time to metastasis, tumor size and Gleason scores.

Hidden clues in prostate cancer - Lessons learned from clinical and pre-clinical approaches on diagnosis and risk stratification.

The heterogeneity of prostate cancer is evident at clinical, morphological and molecular levels. To aid clinical decision making, a three-tiered system for risk stratification is used to designate low-, intermediate-, and high-risk of disease progression. Intermediate-risk prostate cancers are the most frequently diagnosed, and even with common diagnostic features, can exhibit vastly different clinical progression. Thus, improved risk stratification methods are needed to better predict patient outcomes. Here, we provide an overview of the improvements in diagnosis/prognosis arising from advances in pathology reporting of prostate cancer, which can improve risk stratification, especially for patients with intermediate-risk disease. This review discusses updates to pathology reporting of morphological growth patterns, and proposes the utility of integrating prognostic biomarkers or innovative imaging techniques to enhance clinical decision-making. To complement clinical studies, experimental approaches using patient-derived tumors have highlighted important cellular and morphological features associated with aggressive disease that may impact treatment response. The intersection of urology, pathology and scientific disciplines is required to work towards a common goal of understanding disease pathogenesis, improving the stratification of patients with intermediate-risk disease and subsequently defining optimal treatment strategies using precision-based approaches.

Neuroendocrine cells in prostate cancer correlate with poor outcomes: a systematic review and meta-analysis.

OBJECTIVES: To perform a systematic review and meta-analysis of the literature to understand the variation in the reporting of neuroendocrine staining and determine the influence of reporting neuroendocrine staining at diagnosis on patient outcomes. METHODS: Medical databases were searched to identify studies in which adenocarcinoma specimens were stained with any of the following four neuroendocrine markers: chromogranin A (CgA), neuron-specific enolase (NSE), synaptophysin and CD56. The prevalence of neuroendocrine staining and correlation of the prevalence of neuroendocrine staining to patient outcomes were analysed using a random-effects model. All statistical tests were two-sided. RESULTS: Sixty-two studies spanning 7616 patients were analysed. The pooled prevalence for the most common marker, CgA (41%), was similar to that of NSE (39%) and higher than that of synaptophysin (31%). The prevalence of CgA staining was significantly influenced by reporting criteria, where objective thresholds reduced the variation in prevalence to 26%. No correlation was found between CgA prevalence and tumour grade. Patients positive for CgA staining using objective criteria had more rapid biochemical progression (hazard ratio [HR] 1.98, 95% confidence interval [CI] 1.49 to 2.65) and poorer prostate cancer-specific survival (HR 7.03, 95% CI 2.55 to 19.39) compared to negative patients, even among those with low-risk cancers. CONCLUSION: Discrepancies in the reported prevalence of neuroendocrine cells in adenocarcinoma are driven by the inconsistent scoring criteria. This study unequivocally demonstrates that when neuroendocrine cell staining is assessed with objective criteria it identifies patients with poor clinical outcomes. Future studies are needed to determine the exact quantifiable thresholds for use in reporting neuroendocrine cell staining to identify patients at higher risk of progression.

Expanding the clinicopathological spectrum of succinate dehydrogenase-deficient renal cell carcinoma with a focus on variant morphologies: a study of 62 new tumors in 59 patients.

Most succinate dehydrogenase (SDH)-deficient renal cell carcinomas (RCCs) demonstrate stereotypical morphology characterized by bland eosinophilic cells with frequent intracytoplasmic inclusions. However, variant morphologic features have been increasingly recognized. We therefore sought to investigate the incidence and characteristics of SDH-deficient RCC with variant morphologies. We studied a multi-institutional cohort of 62 new SDH-deficient RCCs from 59 patients. The median age at presentation was 39 years (range 19-80), with a slight male predominance (M:F = 1.6:1). A relevant family history was reported in 9 patients (15%). Multifocal or bilateral tumors were identified radiologically in 5 patients (8%). Typical morphology was present at least focally in 59 tumors (95%). Variant morphologies were seen in 13 (21%) and included high-grade nuclear features and various combinations of papillary, solid, and tubular architecture. Necrosis was present in 13 tumors, 7 of which showed variant morphology. All 62 tumors demonstrated loss of SDHB expression by immunohistochemistry. None showed loss of SDHA expression. Germline SDH mutations were reported in all 18 patients for whom the results of testing were known. Among patients for whom follow-up data was available, metastatic disease was reported in 9 cases, 8 of whom had necrosis and/or variant morphology in their primary tumor. Three patients died of disease. In conclusion, variant morphologies and high-grade nuclear features occur in a subset of SDH-deficient RCCs and are associated with more aggressive behavior. We therefore recommend grading all SDH-deficient RCCs and emphasize the need for a low threshold for performing SDHB immunohistochemistry in any difficult to classify renal tumor, particularly if occurring at a younger age.

The MURAL collection of prostate cancer patient-derived xenografts enables discovery through preclinical models of uro-oncology.

Preclinical testing is a crucial step in evaluating cancer therapeutics. We aimed to establish a significant resource of patient-derived xenografts (PDXs) of prostate cancer for rapid and systematic evaluation of candidate therapies. The PDX collection comprises 59 tumors collected from 30 patients between 2012-2020, coinciding with availability of abiraterone and enzalutamide. The PDXs represent the clinico-pathological and genomic spectrum of prostate cancer, from treatment-naïve primary tumors to castration-resistant metastases. Inter- and intra-tumor heterogeneity in adenocarcinoma and neuroendocrine phenotypes is evident from bulk and single-cell RNA sequencing data. Organoids can be cultured from PDXs, providing further capabilities for preclinical studies. Using a 1 x 1 x 1 design, we rapidly identify tumors with exceptional responses to combination treatments. To govern the distribution of PDXs, we formed the Melbourne Urological Research Alliance (MURAL). This PDX collection is a substantial resource, expanding the capacity to test and prioritize effective treatments for prospective clinical trials in prostate cancer.

SP142 PD-L1 Scoring Shows High Interobserver and Intraobserver Agreement in Triple-negative Breast Carcinoma But Overall Low Percentage Agreement With Other PD-L1 Clones SP263 and 22C3.

SP142 programmed cell death ligand 1 (PD-L1) status predicts response to atezolizumab in triple-negative breast carcinoma (TNBC). Prevalence of VENTANA PD-L1 (SP142) Assay positivity, concordance with the VENTANA PD-L1 (SP263) Assay and Dako PD-L1 IHC 22C3 pharmDx assay, and association with clinicopathologic features were assessed in 447 TNBCs. SP142 PD-L1 intraobserver and interobserver agreement was investigated in a subset of 60 TNBCs, with scores enriched around the 1% cutoff. The effect of a 1-hour training video on pretraining and posttraining scores was ascertained. At a 1% cutoff, 34.2% of tumors were SP142 PD-L1 positive. SP142 PD-L1 positivity was significantly associated with tumor-infiltrating lymphocytes (P <0.01), and node negativity (P=0.02), but not with tumor grade (P=0.35), tumor size (P=0.58), or BRCA mutation (P=0.53). Overall percentage agreement (OPA) for intraobserver and interobserver agreement was 95.0% and 93.7%, respectively, among 5 pathologists trained in TNBC SP142 PD-L1 scoring. In 5 TNBC SP142 PD-L1-naive pathologists, significantly higher OPA to the reference score was achieved after video training (posttraining OPA 85.7%, pretraining OPA 81.5%, P<0.05). PD-L1 status at a 1% cutoff was assessed by SP142 and SP263 in 420 cases, and by SP142 and 22C3 in 423 cases, with OPA of 88.1% and 85.8%, respectively. The VENTANA PD-L1 (SP142) Assay is reproducible for classifying TNBC PD-L1 status by trained observers; however, it is not analytically equivalent to the VENTANA PD-L1 (SP263) Assay and Dako PD-L1 IHC 22C3 pharmDx assay.

Androgen receptor enhancer amplification in matched patient-derived xenografts of primary and castrate-resistant prostate cancer.

Amplifications of the androgen receptor (AR) occur in up to 80% of men with castration-resistant prostate cancer (CRPC). Recent studies highlighted that these amplifications not only span the AR gene but usually encompass a distal enhancer. This represents a newly recognised, non-coding mechanism of resistance to AR-directed therapies, including enzalutamide. To study disease progression before and after AR amplification, we used tumour samples from a castrate-sensitive primary tumour and castrate-resistant metastasis of the same patient. For subsequent functional and genomic studies, we established serially transplantable patient-derived xenografts (PDXs). Whole genome sequencing showed that alterations associated with poor prognosis, such as TP53 and PTEN loss, existed before androgen deprivation therapy, followed by co-amplification of the AR gene and enhancer after the development of metastatic CRPC. The PDX of the primary tumour, without the AR amplification, was sensitive to AR-directed treatments, including castration, enzalutamide, and apalutamide. The PDX of the metastasis, with the AR amplification, had higher AR and AR-V7 expression in castrate conditions, and was resistant to castration, apalutamide, and enzalutamide in vivo. Treatment with a BET inhibitor outperformed the AR-directed therapies for the metastasis, resulting in tumour regression for some, but not all, grafts. Therefore, this study provides novel matched PDXs to test potential treatments that target the overabundance of AR in tumours with AR enhancer amplifications. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Knowing what's growing: Why ductal and intraductal prostate cancer matter.

Prostate cancer is a common malignancy, but only some tumors are lethal. Accurately identifying these tumors will improve clinical practice and instruct research. Aggressive cancers often have distinctive pathologies, including intraductal carcinoma of the prostate (IDC-P) and ductal adenocarcinoma. Here, we review the importance of these pathologies because they are often overlooked, especially in genomics and preclinical testing. Pathology, genomics, and patient-derived models show that IDC-P and ductal adenocarcinoma accompany multiple markers of poor prognosis. Consequently, "knowing what is growing" will help translate preclinical research to pinpoint and treat high-risk prostate cancer in the clinic.

Intraductal carcinoma of the prostate is an aggressive form of invasive carcinoma and should be graded.

Infiltration of the prostatic ducts by prostatic adenocarcinoma occurs relatively frequently, being most commonly associated with high grade disease. It is now recognised that intraductal carcinoma of the prostate (IDCP) has an associated poor prognosis and this is reflected in its histological, molecular and immunohistochemical features. The current recommendation of the World Health Organization is that IDCP not be taken into consideration when grading prostate adenocarcinoma. It is apparent that Gleason did not differentiate between IDCP and stromal invasive carcinoma when developing and validating his grading system, and recent studies suggest that the incorporation of IDCP grading into the overall grading of the specimen provides additional prognostic information.

Controversial issues in Gleason and International Society of Urological Pathology (ISUP) prostate cancer grading: proposed recommendations for international implementation.

The Gleason Grading system has been used for over 50 years to prognosticate and guide the treatment for patients with prostate cancer. At consensus conferences in 2005 and 2014 under the guidance of the International Society of Urological Pathology (ISUP), the system has undergone major modifications to reflect modern diagnostic and therapeutic practices. The 2014 consensus conference yielded recommendations regarding cribriform, mucinous, glomeruloid and intraductal patterns, the most significant of which was the removal of any cribriform pattern from Gleason grade 3. Furthermore, a Gleason score grouping system was endorsed which consisted of five grades where Gleason score 6 (3+3) was classified as grade 1 which better reflected the mostly indolent behaviour of these tumours. Another issue discussed at the meeting and subsequently endorsed was that in Gleason score 7 cases, the percentage pattern 4 should be recorded. This is especially important in situations where modern active surveillance protocols expand to include men with low volume pattern 4. While major progress was made at the conference, several issues were either not resolved or not discussed at all. Most of these items relate to details of assignment of Gleason score and ISUP grade in specific specimen types and grading scenarios. This detailed review looks at the 2014 ISUP conference results and subsequent literature from an international perspective and proposes several recommendations. The specific issues addressed are percentage pattern 4 in Gleason score 7 tumours, percentage patterns 4 and 5 or 4/5 in Gleason score 8-10 disease, minor (≤5%) high grade patterns when either 2 or 3 patterns are present, level of reporting (core, specimen, case), dealing with grade diversity among site (highest and composite scores) and reporting scores in radical prostatectomy specimens with multifocal disease. It is recognised that for many of these issues, a strong evidence base does not exist, and further research studies are required. The proposed recommendations mostly reflect consolidated expert opinion and they are classified as established if there was prior agreement by consensus and provisional if there was no previous agreement or if the item was not discussed at prior consensus conferences. For some items there are reporting options that reflect the local requirements and diverse practice models of the international urological pathology community. The proposed recommendations provide a framework for discussion at future consensus meetings.

Establishing a cryopreservation protocol for patient-derived xenografts of prostate cancer.

BACKGROUND: Serially transplantable patient-derived xenografts (PDXs) are invaluable preclinical models for studying tumor biology and evaluating therapeutic agents. As these models are challenging to establish from prostate cancer specimens, the ability to preserve them through cryopreservation has several advantages for ongoing research. Despite this, there is still uncertainty about the ability to cryopreserve PDXs of prostate cancer. This study compared three different cryopreservation protocols to identify a method that can be used to reproducibly cryopreserve a diverse cohort of prostate cancer PDX models. METHODS: One serially transplantable prostate cancer PDX from the Melbourne Urological Research Alliance cohort was used to compare three cryopreservation protocols: slow freezing in fetal calf serum (FCS) with 10% dimethyl sulfoxide (DMSO), FCS with 10% DMSO supplemented with the Rho-associated kinase (ROCK) inhibitor Y-27632 and vitrification. The efficiency of the slow freezing protocols was then assessed in 17 additional prostate cancer PDXs. Following cryopreservation, PDXs were re-established in host mice that were either intact and supplemented with testosterone or castrated. Graft take rate, tumor growth, histological features, and transcriptome profiles before and after cryopreservation were compared. RESULTS: Slow freezing maintained the viability and histological features of prostate cancer PDXs, and the addition of a ROCK inhibitor increased their growth following cryopreservation. Using the slow freezing method, we re-established 100% of PDXs grown in either testosterone-supplemented or castrated host mice. Importantly, the long-term tumor growth rate and transcriptome profile were maintained following cryopreservation. CONCLUSION: This study has identified a protocol to reliably cryopreserve and re-establish a diverse cohort of serially transplantable PDXs of prostate cancer. This study has the potential to significantly improve the practicality of maintaining PDX models. Cryopreservation may also increase the accessibility of these important resources and provide new opportunities for preclinical studies on a broader spectrum of prostate tumors.

Intraclonal Plasticity in Mammary Tumors Revealed through Large-Scale Single-Cell Resolution 3D Imaging.

Breast tumors are inherently heterogeneous, but the evolving cellular organization through neoplastic progression is poorly understood. Here we report a rapid, large-scale single-cell resolution 3D imaging protocol based on a one-step clearing agent that allows visualization of normal tissue architecture and entire tumors at cellular resolution. Imaging of multicolor lineage-tracing models of breast cancer targeted to either basal or luminal progenitor cells revealed profound clonal restriction during progression. Expression profiling of clones arising in Pten/Trp53-deficient tumors identified distinct molecular signatures. Strikingly, most clones harbored cells that had undergone an epithelial-to-mesenchymal transition, indicating widespread, inherent plasticity. Hence, an integrative pipeline that combines lineage tracing, 3D imaging, and clonal RNA sequencing technologies offers a comprehensive path for studying mechanisms underlying heterogeneity in whole tumors.

Patient-derived Models of Abiraterone- and Enzalutamide-resistant Prostate Cancer Reveal Sensitivity to Ribosome-directed Therapy.

BACKGROUND: The intractability of castration-resistant prostate cancer (CRPC) is exacerbated by tumour heterogeneity, including diverse alterations to the androgen receptor (AR) axis and AR-independent phenotypes. The availability of additional models encompassing this heterogeneity would facilitate the identification of more effective therapies for CRPC. OBJECTIVE: To discover therapeutic strategies by exploiting patient-derived models that exemplify the heterogeneity of CRPC. DESIGN, SETTING, AND PARTICIPANTS: Four new patient-derived xenografts (PDXs) were established from independent metastases of two patients and characterised using integrative genomics. A panel of rationally selected drugs was tested using an innovative ex vivo PDX culture system. INTERVENTION: The following drugs were evaluated: AR signalling inhibitors (enzalutamide and galeterone), a PARP inhibitor (talazoparib), a chemotherapeutic (cisplatin), a CDK4/6 inhibitor (ribociclib), bromodomain and extraterminal (BET) protein inhibitors (iBET151 and JQ1), and inhibitors of ribosome biogenesis/function (RNA polymerase I inhibitor CX-5461 and pan-PIM kinase inhibitor CX-6258). OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Drug efficacy in ex vivo cultures of PDX tissues was evaluated using immunohistochemistry for Ki67 and cleaved caspase-3 levels. Candidate drugs were also tested for antitumour efficacy in vivo, with tumour volume being the primary endpoint. Two-tailed t tests were used to compare drug and control treatments. RESULTS AND LIMITATIONS: Integrative genomics revealed that the new PDXs exhibited heterogeneous mechanisms of resistance, including known and novel AR mutations, genomic structural rearrangements of the AR gene, and a neuroendocrine-like AR-null phenotype. Despite their heterogeneity, all models were sensitive to the combination of ribosome-targeting agents CX-5461 and CX-6258. CONCLUSIONS: This study demonstrates that ribosome-targeting drugs may be effective against diverse CRPC subtypes including AR-null disease, and highlights the potential of contemporary patient-derived models to prioritise treatment strategies for clinical translation. PATIENT SUMMARY: Diverse types of therapy-resistant prostate cancers are sensitive to a new combination of drugs that inhibit protein synthesis pathways in cancer cells.