Combining Homologous Recombination-Deficient Testing and Functional RAD51 Analysis Enhances the Prediction of Poly(ADP-Ribose) Polymerase Inhibitor Sensitivity.

PURPOSE: To meet the urgent need for accessible homologous recombination-deficient (HRD) test options, we validated a laboratory-developed test (LDT) and a functional RAD51 assay to assess patients with ovarian cancer and predict the clinical benefit of poly(ADP-ribose) polymerase inhibitor therapy. METHODS: Optimization of the LDT cutoff and validation on the basis of samples from 91 patients enrolled in the ENGOT-ov24/NSGO-AVANOVA1&2 trial (ClinicalTrials.gov identifier: NCT02354131), previously subjected to commercial CDx HRD testing (CDx). RAD51 foci analysis was performed and tumors with ≥five foci/nucleus were classified as RAD51-positive (homologous recombination-proficient). RESULTS: The optimal LDT cutoff is 54. Comparing CDx genome instability score and LDT HRD scores show a Spearman's correlation of rho = 0.764 (P < .0001). Cross-tabulation analysis shows that the sensitivity of the LDT HRD score is 86% and of the LDT HRD status is 91.8% (Fisher's exact test P < .001). Survival analysis on progression-free survival (PFS) of LDT-assessed patients show a Cox regression P < .05. RAD51 assays show a correlation between low RAD51 foci detection (<20% RAD51+ cells) and significantly prolonged PFS (P < .001). CONCLUSION: The robust concordance between the open standard LDT and the CDx, especially the correlation with PFS, warrants future validation and implementation of the open standard LDT for HRD testing in diagnostic settings.

Recurrent events after acute ST-segment elevation myocardial infarction: predictors and features of plaque progression and stent failure.

OBJECTIVES: Patients with acute ST-segment elevation myocardial infarction (STEMI) are at high risk for recurrent coronary events (RCE). Non-culprit plaque progression and stent failure are the main causes of RCEs. We sought to identify the incidence and predictors of RCEs. METHODS: Eight hundred thirty patients with STEMI were enrolled and followed up for 5 years. All patients underwent blood test analysis at hospital admission, at 1-month and at 12-month follow-up times. Patients were divided into RCE group and control group. RCE group was further categorized into non-culprit plaque progression and stent failure subgroups. RESULTS: Among 830 patients with STEMI, 63 patients had a RCE (7.6%). At hospital admission, HDL was numerically lower in RCE group, while LDL at both 1-month and 12-month follow-up times were significantly higher in RCE group. Both HDL at hospital admission and LDL at 12-month follow-up were independently associated with RCEs (OR 0.90, 95% CI 0.81-0.99 and OR 1.041, 95% CI 1.01-1.07, respectively). RCEs were due to non-culprit plaque progression in 47.6% of cases, while in 36.5% due to stent failure. The mean time frame between pPCI and RCE was significantly greater for non-culprit plaque progression subgroup as compared to stent failure subgroup (27 ±â€…18 months and 16 ±â€…14 months, P  = 0.032). CONCLUSION: RCEs still affect patients after pPCI. Low levels of HDL at admission and high levels of LDL at 12 months after pPCI significantly predicted RCEs. A RCE results in non-culprit plaque progression presents much later than an event due to stent failure.

Information-theoretical analysis of the neural code for decoupled face representation.

Processing faces accurately and efficiently is a key capability of humans and other animals that engage in sophisticated social tasks. Recent studies reported a decoupled coding for faces in the primate inferotemporal cortex, with two separate neural populations coding for the geometric position of (texture-free) facial landmarks and for the image texture at fixed landmark positions, respectively. Here, we formally assess the efficiency of this decoupled coding by appealing to the information-theoretic notion of description length, which quantifies the amount of information that is saved when encoding novel facial images, with a given precision. We show that despite decoupled coding describes the facial images in terms of two sets of principal components (of landmark shape and image texture), it is more efficient (i.e., yields more information compression) than the encoding in terms of the image principal components only, which corresponds to the widely used eigenface method. The advantage of decoupled coding over eigenface coding increases with image resolution and is especially prominent when coding variants of training set images that only differ in facial expressions. Moreover, we demonstrate that decoupled coding entails better performance in three different tasks: the representation of facial images, the (daydream) sampling of novel facial images, and the recognition of facial identities and gender. In summary, our study provides a first principle perspective on the efficiency and accuracy of the decoupled coding of facial stimuli reported in the primate inferotemporal cortex.

Ultrasonographic diagnosis of adnexal masses: interobserver agreement in the interpretation of videos, using IOTA terminology.

OBJECTIVES: Aim of this study is to estimate interobserver agreement in classifying adnexal tumors using IOTA terms, simple rules and subjective assessment. In addition, we related observers' accuracy with their experience in gynecological ultrasonography and the year of IOTA certification. METHODS: Eleven observers with three different levels of experience evaluated videoclips of 70 adnexal masses, defining tumor type according to IOTA terms and definitions, classifying the mass using IOTA Simple rules and Subjective assessment as well as providing Color Score evaluation. Sensitivity, specificity and area under the ROC curve were calculated and the year of IOTA certification was related with operators' accuracy through Pearson correlation coefficient. Interobserver agreement was estimated calculating percentage of agreement, Fleiss kappa and Cohen's kappa. RESULTS: We found a positive correlation between the year of IOTA certification and operators' accuracy (Pearson coefficient 0.694), especially among the observers with the least experience, the residents (p = 0.003). For tumor type classification, identification of papillary projections and classification of tumors using subjective assessment, agreement among all observers was moderate (Fleiss kappa 0.455, 0.552, and 0.476, respectively) and increased with the years of experience. Agreement in the application of Simple Rules was moderate in all examiners with IOTA certification, with Fleiss kappa in the range of (0.403, 0.498). For Color Score assignment interobserver agreement among all observers was fair (Cohen's kappa 0.380). CONCLUSIONS: Even among expert examiners, the results of adnexal lesion assessment can be inconsistent. Experience impacts on accuracy and agreement in subjective assessment, while the application of Simple Rules can mitigate the role of experience in interobserver agreement. The knowledge of IOTA models among residents seams to improve their diagnostic accuracy, showing the benefits of IOTA terminology for in training sonographers.

Uterine smooth muscle tumors: a multicenter, retrospective, comparative study of clinical and ultrasound features.

OBJECTIVE: To evaluate a wide range of clinical and ultrasound characteristics of different uterine smooth muscle tumors to identify features capable of discriminating between these types. METHODS: This was a retrospective, multicenter study that included 285 patients diagnosed with uterine smooth muscle tumors (50 leiomyosarcomas, 35 smooth muscle tumors of uncertain malignant potential, and 200 leiomyomas). The patients were divided into three groups based on the histological type of their tumors, and the groups were compared according to the variables collected. RESULTS: Leiomyosarcomas were more common in older and post-menopausal women. Compared with leiomyomas, smooth muscle tumors of uncertain malignant potential and leiomyosarcomas had similar ultrasound features such as absence of normal myometrium, multilocular appearance, hyper-echogenicity in case of uniform echogenicity, absence of posterior shadows, echogenic areas, and hyperechoic rim. Leiomyosarcomas were larger, had more cystic areas, and were associated with a higher prevalence of pelvic free fluid. Smooth muscle tumors of uncertain malignant potential were characterized by a higher frequency of International Federation of Gynecology and Obstetrics (FIGO) type 6-7, the absence of internal shadows, and, in the case of cystic area, the presence of a regular internal wall. Tumor outline varied among the three histological types. A color score of 1 was typical of leiomyoma, a color score 2 was mainly observed in leiomyomas and smooth muscle tumors of uncertain malignant potential, a color score 3 did not differ among the tumors, while a color of score 4 was related to leiomyosarcomas. When combining color scores 3 and 4, leiomyosarcomas and smooth muscle tumors of uncertain malignant potential showed a high percentage of both circumferential and intra-lesional vascularization. A cooked appearance was not statistically different among the tumors. CONCLUSIONS: Based on our findings, specific ultrasonographic features as well as age and menopausal status are associated with different uterine smooth muscle tumor types. Integration of these data can help the pre-operative assessment of these lesions for proper management.

Availability and type of energy regulate the global distribution of neritic carbonates.

The study of carbonate rocks is primarily reliant on microfacies analysis, which is strongly based on the comparison with modern allochem assemblages. Despite the existence of several models aimed at comprehensively explaining, on the bases of abiotic factors, the distribution of carbonate-producing organisms, a global, quantitative and standardized overview of the composition of shallow-water carbonate sediments is still missing. Aiming to address this gap in knowledge, the current study provides a global database of the available quantitative data on neritic carbonate sediments. This is paired with satellite-based observations for the abiotic parameters. The results highlight a non-linear, multi-variable, dependence in the distribution of allochems and suggest that depth, temperature, and trophic state are, to a certain extent, interchangeable. The implication of which is a level of non-uniqueness for paleoenvironmental interpretation. The resulting distribution is rather continuous and stretches along an energy gradient. A gradient extending from solar energy, with autotrophs and symbiont-bearing organisms to chemical energy with heterotrophs. Further, quantitative data from modern oceans are still required to disentangle the remaining elements of uncertainty.

A stem cell epigenome is associated with primary nonresponse to CD19 CAR T cells in pediatric acute lymphoblastic leukemia.

CD19 chimeric antigen receptor T-cell therapy (CD19-CAR) has changed the treatment landscape and outcomes for patients with pre-B-cell acute lymphoblastic leukemia (B-ALL). Unfortunately, primary nonresponse (PNR), sustained CD19+ disease, and concurrent expansion of CD19-CAR occur in 20% of the patients and is associated with adverse outcomes. Although some failures may be attributable to CD19 loss, mechanisms of CD19-independent, leukemia-intrinsic resistance to CD19-CAR remain poorly understood. We hypothesize that PNR leukemias are distinct compared with primary sensitive (PS) leukemias and that these differences are present before treatment. We used a multiomic approach to investigate this in 14 patients (7 with PNR and 7 with PS) enrolled in the PLAT-02 trial at Seattle Children's Hospital. Long-read PacBio sequencing helped identify 1 PNR in which 47% of CD19 transcripts had exon 2 skipping, but other samples lacked CD19 transcript abnormalities. Epigenetic profiling discovered DNA hypermethylation at genes targeted by polycomb repressive complex 2 (PRC2) in embryonic stem cells. Similarly, assays of transposase-accessible chromatin-sequencing revealed reduced accessibility at these PRC2 target genes, with a gain in accessibility of regions characteristic of hematopoietic stem cells and multilineage progenitors in PNR. Single-cell RNA sequencing and cytometry by time of flight analyses identified leukemic subpopulations expressing multilineage markers and decreased antigen presentation in PNR. We thus describe the association of a stem cell epigenome with primary resistance to CD19-CAR therapy. Future trials incorporating these biomarkers, with the addition of multispecific CAR T cells targeting against leukemic stem cell or myeloid antigens, and/or combined epigenetic therapy to disrupt this distinct stem cell epigenome may improve outcomes of patients with B-ALL.

Clinical, Sonographic, and Hysteroscopic Features of Endometrial Carcinoma Diagnosed after Hysterectomy in Patients with a Preoperative Diagnosis of Atypical Hyperplasia: A Single-Center Retrospective Study.

BACKGROUND: atypical endometrial hyperplasia (AEH) is a precancerous condition implying a high risk of concurrent endometrial cancer (EC), which might be occult and only diagnosed at postoperative histopathological examination after hysterectomy. Our study aimed to investigate potential differences in preoperative clinical, sonographic, and hysteroscopic characteristics in patients with AEH and postoperative diagnosis of EC. METHODS: a retrospective single-center study was carried out on a case series of 80 women with AEH undergoing diagnostic workup, including ultrasonography and hysteroscopy, with subsequent hysterectomy. Women with AEH confirmed at the histopathological examination were compared with patients with a postoperative diagnosis of EC. RESULTS: in our population, EC was diagnosed in 53 women, whereas the preoperative diagnosis of AEH was confirmed in 27 cases. At ultrasonography, women with occult EC showed greater endometrial thickness (20.3 mm vs. 10.3 mm, p 0.001) and size of the endocavitary lesion (maximum diameter 25.2 mm vs. 10.6 mm, p 0.001), and a higher prevalence of irregular endometrial-myometrial junction (40.5% vs. 6.7%, p 0.022) and endouterine vascularization at color Doppler (64.2% vs. 34.6%, p 0.017). At hysteroscopy, patients with occult EC showed a higher prevalence of necrosis (44.2% vs. 4.2%, p 0.001) and atypical vessels (70.6% vs. 33.3%, p 0.003), whereas true AEH mainly presented as a protruding intracavitary lesion (77.8% vs. 50.9%, p 0.029). In EC, subjective assessment by the operator was more frequently indicative of cancer (80.0% vs. 12.5%). No difference was found for clinical variables. CONCLUSIONS: occult EC in AEH may exhibit some differences in ultrasonographic and hysteroscopic patterns of presentation compared with real AEH, which could prompt a more significant suspect for the possible presence of concurrent EC at preoperative diagnostic workup.

Progesterone Receptor Modulates Extraembryonic Mesoderm and Cardiac Progenitor Specification during Mouse Gastrulation.

Progesterone treatment is commonly employed to promote and support pregnancy. While maternal tissues are the main progesterone targets in humans and mice, its receptor (PGR) is expressed in the murine embryo, questioning its function during embryonic development. Progesterone has been previously associated with murine blastocyst development. Whether it contributes to lineage specification is largely unknown. Gastrulation initiates lineage specification and generation of the progenitors contributing to all organs. Cells passing through the primitive streak (PS) will give rise to the mesoderm and endoderm. Cells emerging posteriorly will form the extraembryonic mesodermal tissues supporting embryonic growth. Cells arising anteriorly will contribute to the embryonic heart in two sets of distinct progenitors, first (FHF) and second heart field (SHF). We found that PGR is expressed in a posterior-anterior gradient in the PS of gastrulating embryos. We established in vitro differentiation systems inducing posterior (extraembryonic) and anterior (cardiac) mesoderm to unravel PGR function. We discovered that PGR specifically modulates extraembryonic and cardiac mesoderm. Overexpression experiments revealed that PGR safeguards cardiac differentiation, blocking premature SHF progenitor specification and sustaining the FHF progenitor pool. This role of PGR in heart development indicates that progesterone administration should be closely monitored in potential early-pregnancy patients undergoing infertility treatment.

Comparative chromatin accessibility upon BDNF stimulation delineates neuronal regulatory elements.

Neuronal stimulation induced by the brain-derived neurotrophic factor (BDNF) triggers gene expression, which is crucial for neuronal survival, differentiation, synaptic plasticity, memory formation, and neurocognitive health. However, its role in chromatin regulation is unclear. Here, using temporal profiling of chromatin accessibility and transcription in mouse primary cortical neurons upon either BDNF stimulation or depolarization (KCl), we identify features that define BDNF-specific chromatin-to-gene expression programs. Enhancer activation is an early event in the regulatory control of BDNF-treated neurons, where the bZIP motif-binding Fos protein pioneered chromatin opening and cooperated with co-regulatory transcription factors (Homeobox, EGRs, and CTCF) to induce transcription. Deleting cis-regulatory sequences affect BDNF-mediated Arc expression, a regulator of synaptic plasticity. BDNF-induced accessible regions are linked to preferential exon usage by neurodevelopmental disorder-related genes and the heritability of neuronal complex traits, which were validated in human iPSC-derived neurons. Thus, we provide a comprehensive view of BDNF-mediated genome regulatory features using comparative genomic approaches to dissect mammalian neuronal stimulation.

Clinical and Histopathological Predictors of Recurrence in Uterine Smooth Muscle Tumor of Uncertain Malignant Potential (STUMP): A Multicenter Retrospective Cohort Study of Tertiary Centers.

BACKGROUND: The term uterine smooth muscle tumor of uncertain malignant potential (STUMP) indicates a rare, equivocal entity between benign leiomyomas and leiomyosarcomas. In the present study, we evaluated a comprehensive range of clinical, surgical, and pathological features in a large multicenter series of patients with STUMP to identify risk factors for recurrence. METHODS: This is a retrospective study performed by collecting consecutive cases diagnosed between January 2000 and December 2020 in five tertiary centers. Associations between STUMP recurrence and clinicopathological characteristics as well as surgical treatment modality were investigated. RESULTS: Eighty-seven patients affected by STUMP were considered. Of them, 18 cases (20.7%) recurred: 11 as leiomyosarcoma (LMS) and 7 as STUMP. The mean time to recurrence was 79 months. We found that fragmentation/morcellation, epithelioid features, high mitotic count, Ki-67 value > 20%, progesterone receptor (PR) < 83%, and p16 diffuse expression were associated with higher risk of recurrence and shorter recurrence-free survival (RFS). Furthermore, morcellation/fragmentation and mitotic count remained independent risk factors for recurrence and shorter RFS after multivariate analysis, while the presence of epithelioid features was an independent risk factor for recurrence only. CONCLUSIONS: Our results suggest that morcellation is associated with risk of recurrence and shorter RFS, thus it should be avoided if a STUMP is suspected preoperatively. Epithelioid features, high proliferation activity, low PR expression, and diffuse p16 expression are also unfavorable prognostic factors, so patients presenting these features should be closely followed up.

Low-Grade Uterine Endometrial Stromal Sarcoma: Prognostic Analysis of Clinico-Pathological Characteristics, Surgical Management, and Adjuvant Treatments. Experience From Two Referral Centers.

Objective: Low-grade uterine endometrial stromal sarcoma (LG-ESS) is a rare tumor characterized by an overall good survival but showing a indolent behavior and a variable risk of recurrence. There is no clear consensus on the optimal management of these tumors and no prognostic or predictive factors have been established. With this study, we evaluated the prognostic relevance of several clinical, surgical, and pathological features in patients affected by LG-ESS to identify risk factors associated with recurrence. Methods: We retrospectively analyzed 52 LG-ESS cases, treated from January 1st, 1994, to May 31st, 2020, in two referral centers. The relationship between recurrence and clinicopathological characteristics as well as surgical treatment was investigated. Risk of recurrence and disease-free survival (DFS) were estimated by Cox regression and the Kaplan-Meier analysis, respectively. Results: Of 52 patients with LG-ESS, 8 experienced recurrence (15%). The median follow-up was 100 months (SD ± 96, range: 15-336). By univariate analysis, fragmentation/morcellation, tumor size, FIGO stage, higher mitotic count, presence of necrosis, and lymphovascular space invasion (LSVI) resulted associated with a poorer outcome. Conversely, the surgical modality (laparotomic vs laparoscopic and hysterectomy with bilateral salpingo-oophorectomy vs local excision) and pelvic lymphadenectomy were not. Even the different modalities of adjuvant therapy (hormonal therapy, radiotherapy, and chemotherapy) showed no prognostic significance. Tumor fragmentation/morcellation and higher mitotic count resulted independent prognostic variables at multivariate analysis. Conclusions: This data supports the avoidance of any type of morcellation if LG-ESS is suspected preoperatively. Higher mitotic count and, possibly, tumor size, advanced FIGO stage, necrosis, and LVSI could be exploited to tailor the adjuvant therapy, but these results need to be confirmed in larger prospective studies.

Long-term Results of Perfusion-Balloon Valvuloplasty, Without Rapid Pacing, in High-Risk Elderly Patients With Severe Aortic Stenosis: A New Space Oddity.

BACKGROUND: Percutaneous balloon aortic valvuloplasty (BAV) is actually recommended as a bridge to surgery or transcatheter aortic valve replacement in patients with severe aortic stenosis (AS) in particular clinical settings. In this pilot study, for the first time, we report our experience utilizing a nonocclusive balloon for BAV, which does not require rapid ventricular pacing (RVP), in high-risk symptomatic elderly patients with severe AS. METHODS AND RESULTS: From 2018 to 2020, a total of 30 high-risk elderly patients with heart failure due to severe AS were treated with BAV and were all prospectively included in the study. We used a perfusion-balloon valvuloplasty without RVP (True Flow; BD/Bard). Hemodynamic parameters were invasively evaluated during catheterization, before and immediately after BAV. All patients were regularly followed to detect the rate of mortality. The patients were 87.56 ± 4.10 years old and 23% were males. In the catheterization laboratory, the peak left ventricular to aortic pressure gradient significantly decreased from 55 mm Hg (interquartile range [IQR], 48.75-66.25) to 26 mm Hg (IQR, 15.7-30) immediately after balloon inflation (P<.001). The median value of percentage decrease of transaortic gradient was 56% (IQR, 50-74). At a median of 12 months (IQR, 5-27) follow-up, 12 patients (40%) died. The median time between BAV and mortality was 10.5 months (IQR, 1.75-15.5). At multivariable analysis, the only predictor of mortality was the New York Heart Association class at admission (odds ratio, 3.29; 95% confidence interval, 2.4-298.4; P<.01). CONCLUSION: This single-center pilot study represents the first evidence that perfusion-balloon valvuloplasty without RVP is a safe, valid, and durable option in high-risk, symptomatic, elderly patients with severe AS.

EP300 Selectively Controls the Enhancer Landscape of MYCN-Amplified Neuroblastoma.

Gene expression is regulated by promoters and enhancers marked by histone H3 lysine 27 acetylation (H3K27ac), which is established by the paralogous histone acetyltransferases (HAT) EP300 and CBP. These enzymes display overlapping regulatory roles in untransformed cells, but less characterized roles in cancer cells. We demonstrate that the majority of high-risk pediatric neuroblastoma (NB) depends on EP300, whereas CBP has a limited role. EP300 controls enhancer acetylation by interacting with TFAP2ß, a transcription factor member of the lineage-defining transcriptional core regulatory circuitry (CRC) in NB. To disrupt EP300, we developed a proteolysis-targeting chimera (PROTAC) compound termed "JQAD1" that selectively targets EP300 for degradation. JQAD1 treatment causes loss of H3K27ac at CRC enhancers and rapid NB apoptosis, with limited toxicity to untransformed cells where CBP may compensate. Furthermore, JQAD1 activity is critically determined by cereblon (CRBN) expression across NB cells. SIGNIFICANCE: EP300, but not CBP, controls oncogenic CRC-driven transcription in high-risk NB by binding TFAP2ß. We developed JQAD1, a CRBN-dependent PROTAC degrader with preferential activity against EP300 and demonstrated its activity in NB. JQAD1 has limited toxicity to untransformed cells and is effective in vivo in a CRBN-dependent manner. This article is highlighted in the In This Issue feature, p. 587.

Coronary Plaque Rupture in Stable Coronary Artery Disease and Non-ST Segment Elevation Myocardial Infarction: An Optical Coherence Tomography Study.

BACKGROUND: Plaque rupture (PR) is the main cause of coronary thrombosis in non-ST segment elevation myocardial infarction (NSTEMI), but can be found in stable coronary artery disease (CAD). Our study compared the morphology and local inflammatory activity of ruptured plaques between stable CAD and NSTEMI patients using frequency-domain optical coherence tomography (FD-OCT). METHODS: We retrospectively evaluated 70 plaques with PR at the FD-OCT (25 in stable CAD patients and 45 in NSTEMI patients). Main clinical, angiographic, and morphological features were compared. RESULTS: Besides an overall equivalence in clinical and angiographic features (except for more smokers among NSTEMI patients), some important FD-OCT differences in plaque morphology emerged: PR in NSTEMI was characterized by more macrophage infiltrates (78% in NSTEMI patients vs 20% in stable CAD patients; P<.001) and intraluminal thrombosis (84% in NSTEMI patients vs 48% in stable CAD patients; P<.01). Quantitative analysis showed a higher density of macrophages in NSTEMI than in stable CAD patients: median max normalized standard deviation (NSD) was 0.0934 (IQR, 0.0796-0.1022) vs 0.0689 (IQR, 0.0598-0.0787); P<.01 and mean NSD was 0.062 (IQR, 0.060-0.065) vs 0.053 (IQR, 0.051-0.060); P<.001. Other morphological features did not differ between stable CAD and NSTEMI patients. Main FD-OCT quantitative parameters like minimal lumen area and plaque length were also equivalent between the 2 groups. CONCLUSIONS: Differences in morphological features of PR between stable CAD and NSTEMI patients suggest that local inflammation contributes to the unstable fate of the atherosclerotic plaque.

A ChIP-exo screen of 887 Protein Capture Reagents Program transcription factor antibodies in human cells.

Antibodies offer a powerful means to interrogate specific proteins in a complex milieu. However, antibody availability and reliability can be problematic, whereas epitope tagging can be impractical in many cases. To address these limitations, the Protein Capture Reagents Program (PCRP) generated over a thousand renewable monoclonal antibodies (mAbs) against human presumptive chromatin proteins. However, these reagents have not been widely field-tested. We therefore performed a screen to test their ability to enrich genomic regions via chromatin immunoprecipitation (ChIP) and a variety of orthogonal assays. Eight hundred eighty-seven unique antibodies against 681 unique human transcription factors (TFs) were assayed by ultra-high-resolution ChIP-exo/seq, generating approximately 1200 ChIP-exo data sets, primarily in a single pass in one cell type (K562). Subsets of PCRP mAbs were further tested in ChIP-seq, CUT&RUN, STORM super-resolution microscopy, immunoblots, and protein binding microarray (PBM) experiments. About 5% of the tested antibodies displayed high-confidence target (i.e., cognate antigen) enrichment across at least one assay and are strong candidates for additional validation. An additional 34% produced ChIP-exo data that were distinct from background and thus warrant further testing. The remaining 61% were not substantially different from background, and likely require consideration of a much broader survey of cell types and/or assay optimizations. We show and discuss the metrics and challenges to antibody validation in chromatin-based assays.