Histopathological Analysis of Brains from Dogs Infected with Canine Distemper Virus.

We describe the use of conventional histology and immunohistochemistry against canine distemper virus (CDV) to examine the brains of domestic dogs with a confirmed diagnosis of CDV infection. Histologically, to identify the main typical lesions, we used conventional H&E stain; to evaluate the progressive demyelination, we used Luxol Fast Blue stain; and to identify the presence of viral particles in these affected regions, we used immunohistochemistry against CDV. We confirm that the histopathological analysis of brains of distemper-infected dogs is a powerful tool to evaluate the typical brain lesions and could be used as an interesting natural model to continue studying the pathogenesis of canine distemper in different species and/or other morbillivirus infections, like measles.

Double Chromogen-based Immunohistochemical Staining: An Efficient Approach for Utilizing Long-term Formalin-fixed Tissue in Biobanks.

The New South Wales Brain Tissue Resource Centre is a human brain bank that provides top-quality brain tissue for cutting-edge neuroscience research spanning various conditions from alcohol use disorder to neurodegenerative diseases. However, the conventional practice of preserving brain tissue in formalin poses challenges for immunofluorescent staining primarily due to the formalin's tendency, over time, to create cross-links between antigens, which can obscure epitopes of interest. In addition, researchers can encounter issues such as spectral bleeding, limitations in using multiple colors, autofluorescence, and cross-reactivity when working with long-term formalin-fixed brain tissue. The purpose of the study was to test chromogen-based double immunolabeling to negate the issues with immunofluorescent staining. Colocalization of antigens was explored using chromogens 3-amino-9-ethylcarbazole (AEC) and 3,3,-diaminobenzidine in a sequential staining procedure where the AEC signal was eliminated by alcohol treatment. Combinations of 2 or 3 primary antibodies from the same or different species were trialed successfully with this protocol. The colocalization of antigens was also demonstrated with pseudocoloring that mimicked immunofluorescence staining. This staining technique increases the utility of archival formalin-fixed tissue samples.

Imaging Cell Signaling in Tissues Using the IBEX Method.

The study of cell signaling within tissues can be enhanced using highly multiplexed immunohistochemistry to localize the presence and spatial distribution of numerous pathways of interest simultaneously. Additional data can also be gained by placing the identified proteins into the context of adjacent structures, stroma, and interacting partners. Here, we outline a protocol for using the recently described IBEX method on tissues. This is an open and simple cyclic immunohistochemistry approach suited to this application. We describe a simplified protocol and provide guidance on the method, using a 12-marker panel on human retina to demonstrate the approach.

CytoLyt fixation impedes insulinoma-associated protein 1 (INSM1) immunoreactivity compared to formalin fixation.

INTRODUCTION: Insulinoma-associated protein 1 (INSM1) is an immunohistochemical marker commonly used to confirm cytomorphological concordant neuroendocrine tumors/carcinomas (NETs/NECs), demonstrating high utility in small samples. Previous reports have suggested comparable INSM1 staining in CytoLyt-fixed cell blocks and formalin-fixed surgical pathology specimens. This study aimed to assess INSM1 immunoreactivity using both fixation methods and investigate potential factors contributing to its variable expression. MATERIALS AND METHODS: A retrospective query was performed (03/31/21-05/31/22) for NET/NEC cases that had both formalin- and CytoLyt-fixed cell blocks. We collected clinical data and reporting of immunostains for each case. INSM1 staining was evaluated in both fixation methods, and reported as positive, negative, or equivocal. Equivocal INSM1 staining was further scored as a percentage of 1%-100% and intensity of weak (faint staining), moderate (darker staining), and strong (dense staining). RESULTS: Our search identified 20 cases from diverse body sites, including mediastinal lymph nodes (40%), pancreas (35%), lung (20%), and porta hepatis lymph nodes (5%). All cases exhibited a widespread positivity (over 90%) in formalin-fixed cell blocks. In contrast, CytoLyt fixed cells showed a negative stain in 65% of cases and 30% exhibited an equivocal positivity. CONCLUSIONS: While INSM1 is previously reported as a sensitive (75%-100%) and specific (82.7%-100%) marker for NET/NECs, our study found a reduced immunohistochemical staining in CytoLyt-fixed cell blocks. Consequently, false negative INSM1 immunohistochemical results in CytoLyt-fixed cell block material may pose a pitfall in the diagnosis of NET/NEC.

Illustrated Neuroanatomy of Ctenophores: Immunohistochemistry.

Ctenophores or comb jellies are representatives of an enigmatic lineage of early branching metazoans with complex tissue and organ organization. Their biology and even microanatomy are not well known for most of these fragile pelagic and deep-water species. Here, we present immunohistochemical protocols successfully tested on more than a dozen ctenophores. This chapter also illustrates neural organization in several reference species of the phylum (Pleurobrachia bachei, P. pileus, Mnemiopsis leidyi, Bolinopsis microptera, Beroe ovata, and B. abyssicola) as well as numerous ciliated structures in different functional systems. The applications of these protocols illuminate a very complex diversification of cell types comparable to many bilaterian lineages.

A Multiplexed Approach to Assess Small Cell Lung Cancer Subtype Heterogeneity in Primary and Patient-Derived Tumor Samples.

Unlocking the heterogeneity of cancers is crucial for developing therapeutic approaches that effectively eradicate disease. As our understanding of markers specific to cancer subclones or subtypes expands, there is a growing demand for advanced technologies that enable the simultaneous investigation of multiple targets within an individual tumor sample. Indeed, multiplex approaches offer distinct benefits, particularly when tumor specimens are small and scarce. Here we describe the utility of two fluorescence-based multiplex approaches; fluorescent Western blots, and multiplex immunohistochemistry (Opal™) staining to interrogate heterogeneity, using small cell lung cancer as an example. Critically, the coupling of Opal™ staining with advanced image quantitation, permits the dissection of cancer cell phenotypes at a single cell level. These approaches can be applied to patient biopsies and/or patient-derived xenograft (PDX) models and serve as powerful methodologies for assessing tumor cell heterogeneity in response to therapy or between metastatic lesions across diverse tissue sites.

H-VISTA Immunohistochemistry Score Is Associated with Advanced Stages in Cutaneous and Ocular Melanoma.

Melanoma represents a public health issue. One of the biggest goals of current research is to develop new therapeutic options for patients affected by this aggressive tumor. We conducted a retrospective study including 105 patients diagnosed with cutaneous and ocular melanoma, with stages varying from pT1a to pT4b and pT4e, respectively, and we performed immunohistochemistry reactions with the new potential prognostic marker, VISTA (V-domain Ig suppressor of T cell activation). We quantified the expression by applying the H-score adapted for VISTA and divided the patients, based on the median value, into groups that presented high, low, and negative expression. Therefore, we obtained 65 cases with positive expression for cutaneous melanoma and 8 cases with positive expression for ocular melanoma. Forty-one cases presented high expression in cutaneous melanoma and three cases presented high expression in ocular melanoma. In cutaneous melanoma, analytic statistics showed that VISTA expression was associated with a high Breslow index, high mitotic count, high Ki67 expression, and advanced clinicopathological stage. The majority of ocular melanoma cases demonstrating a positive reaction were classified as stage pT3, whereas earlier stages showed a negative reaction. Our findings underscore a significant correlation between VISTA expression and key prognostic factors in melanoma. Looking ahead, the prospect of future randomized studies holds promise in corroborating the clinical relevance of our findings. By further elucidating the intricate relationship between VISTA expression and melanoma progression, new treatment strategies could be found, improving patient outcomes in this challenging neoplasm.

Morphological Evaluation and Immunohistochemical Analysis of the Reparative Potential of the Buccal Fat Pad.

Background and Objectives: There are many surgical techniques for oroantral communication treatment, one of which is the buccal fat pad. Of particular interest is the high reparative potential of the buccal fat pad, which may be contributed to by the presence of mesenchymal stem cells. The purpose of this work is to evaluate the reparative potential of BFP cells using morphological and immunohistochemical examination. Materials and Methods: 30 BFP samples were provided by the Clinic of Maxillofacial and Plastic Surgery of the Russian University of Medicine (Moscow, Russia) from 28 patients. Morphological examination of 30 BFP samples was performed at the Institute of Clinical Morphology and Digital Pathology of Sechenov University. Hematoxylin-eosin, Masson trichrome staining and immunohistochemical examination were performed to detect MSCs using primary antibodies CD133, CD44 and CD10. Results: During staining with hematoxylin-eosin and Masson's trichrome, we detected adipocytes of white adipose tissue united into lobules separated by connective tissue layers, a large number of vessels of different calibers, as well as the general capsule of BFP. The thin connective tissue layers contained neurovascular bundles. Statistical processing of the results of the IHC examination of the samples using the Mann-Whitney criterion revealed that the total number of samples in which the expression of CD44, CD10 and CD133 antigens was confirmed was statistically significantly higher than the number of samples where the expression was not detected (p < 0.05). Conclusions: During the morphological study of the BFP samples, we revealed statistically significant signs of MSCs presence (p < 0.05), including in the brown fat tissue, which proves the high reparative potential of this type of tissue and can make the BFP a choice option among other autogenous donor materials when eliminating OAC and other surgical interventions in the maxillofacial region.

Uterine Cesarean Scar Tissue-An Immunohistochemical Study.

Background and Objectives: Wound healing encompasses a multitude of factors and entails the establishment of interactions among components of the basement membrane. The quantification of particle concentrations can serve as valuable biomarkers for assessing biomechanical muscle properties. The objective of this study was to examine the immunoexpression and immunoconcentration of myometrial collagen type VI, elastin, alpha-smooth muscle actin, and smooth muscle myosin heavy chain, as well as the expression of platelets and clusters of differentiation 31 in the uterine scar following a cesarean section (CS). Materials and Methods: A total of 177 biopsies were procured from a cohort of pregnant women who were healthy, specifically during the surgical procedure of CS. The participants were categorized into seven distinct groups. Group 1 consisted of primiparas, with a total of 52 individuals. The subsequent groups were organized based on the duration of time that had elapsed since their previous CS. The analysis focused on the immunoexpression and immunoconcentration of the particles listed. Results: No significant variations were observed in the myometrial immunoconcentration of collagen type VI, elastin, smooth muscle myosin, and endothelial cell cluster of differentiation 31 among the analyzed groups. The concentration of alpha-smooth muscle actin in the myometrium was found to be significantly higher in patients who underwent CS within a period of less than 2 years since their previous CS, compared to those with a longer interval between procedures. Conclusions: Our findings indicate that the immunoconcentration of uterine myometrial scar collagen type VI, elastin, smooth muscle myosin heavy chain, alpha-smooth muscle actin, and endothelial cell marker cluster of differentiation 31 remains consistent regardless of the duration elapsed since the previous CS. The findings indicate that there are no significant alterations in the biomechanical properties of the uterine muscle beyond a period of 13 months following a CS.

Shift from Pro- to Anti-Inflammatory Phase in Pelvic Floor Muscles at Postpartum Matches Histological Signs of Regeneration in Multiparous Rabbits.

Background and Objectives: Pelvic floor muscles (PFM) play a core role in defecation and micturition. Weakening of PFM underlies urogynecological disorders such as pelvic organ prolapse and stress urinary incontinence. Vaginal delivery damages PFM. Muscle trauma implies an inflammatory response mediated by myeloid cells, essential for subsequent recovery. Molecular signaling characterizing the pro-inflammatory phase shifts M1 macrophages to M2 macrophages, which modulate muscle repair. The present study aimed to evaluate histological characteristics and the presence of M1 and M2 macrophages in bulbospongiosus (Bsm) and pubococcygeus muscles (Pcm). Materials and Methods: Muscles from young nulliparous (N) and multiparous rabbits on postpartum days three (M3) and twenty (M20) were excised and histologically processed to measure the myofiber cross-sectional area (CSA) and count the centralized myonuclei in hematoxylin-eosinstained sections. Using immunohistochemistry, M1 and M2 macrophages were estimated in muscle sections. Kruskal-Wallis or one-way ANOVA testing, followed by post hoc tests, were conducted to identify significant differences (p < 0.05). Results: The myofiber CSA of both the Bsm and Pcm of the M3 group were more extensive than those of the N and M20 groups. Centralized myonuclei estimated in sections from both muscles of M20 rabbits were higher than those of N rabbits. Such histological outcomes matched significant increases in HLA-DR immunostaining in M3 rabbits with the CD206 immunostaining in muscle sections from M20 rabbits. Conclusions: A shift from the pro- to anti-inflammatory phase in the bulbospongiosus and pubococcygeus muscles of multiparous rabbits matches with centralized myonuclei, suggesting the ongoing regeneration of muscles.

Scoring PD-L1 Expression in Urothelial Carcinoma: An International Multi-Institutional Study on Comparison of Manual and Artificial Intelligence Measurement Model (AIM-PD-L1) Pathology Assessments.

Assessing programmed death ligand 1 (PD-L1) expression on tumor cells (TCs) using Food and Drug Administration-approved, validated immunoassays can guide the use of immune checkpoint inhibitor (ICI) therapy in cancer treatment. However, substantial interobserver variability has been reported using these immunoassays. Artificial intelligence (AI) has the potential to accurately measure biomarker expression in tissue samples, but its reliability and comparability to standard manual scoring remain to be evaluated. This multinational study sought to compare the %TC scoring of PD-L1 expression in advanced urothelial carcinoma, assessed by either an AI Measurement Model (AIM-PD-L1) or expert pathologists. The concordance among pathologists and between pathologists and AIM-PD-L1 was determined. The positivity rate of ≥ 1%TC PD-L1 was between 20-30% for 8/10 pathologists, and the degree of agreement and scoring distribution for among pathologists and between pathologists and AIM-PD-L1 was similar both scored as a continuous variable or using the pre-defined cutoff. Numerically higher score variation was observed with the 22C3 assay than with the 28-8 assay. A 2-h training module on the 28-8 assay did not significantly impact manual assessment. Cases exhibiting significantly higher variability in the assessment of PD-L1 expression (mean absolute deviation > 10) were found to have patterns of PD-L1 staining that were more challenging to interpret. An improved understanding of sources of manual scoring variability can be applied to PD-L1 expression analysis in the clinical setting. In the future, the application of AI algorithms could serve as a valuable reference guide for pathologists while scoring PD-L1.

Automated imaging analysis of Ki-67 immunohistochemistry on whole slide images of cell blocks from pancreatic neuroendocrine neoplasms.

INTRODUCTION: Accurate grading of pancreatic neuroendocrine tumors (PanNETs) relies on the assessment of Ki-67 immunohistochemistry (IHC). While digital imaging analysis (DIA) has been employed for Ki-67 IHC assessment in surgical specimens, its applicability to cytologic specimens remains underexplored. This study aimed to evaluate an automated DIA for assessing Ki-67 IHC on PanNET cell blocks. MATERIALS AND METHODS: The study included 61 consecutive PanNETs and 5 pancreatic neuroendocrine carcinomas. Ki-67 IHC slides from cell blocks were digitally scanned into whole slide images using Philips IntelliSite Scanners and analyzed in batches using the Visiopharm Ki-67 App in a digital workflow. Ki-67 scores obtained through DIA were compared to pathologists' manual scores. RESULTS: The Pearson correlation coefficient of the percentage of Ki-67-stained nuclei between DIA reads and the originally reported reads was 0.9681. Concordance between DIA Ki-67 grades and pathologists' Ki-67 grades was observed in 92.4% (61/66) of cases with the calculated Cohen's Kappa coefficient of 0.862 (almost perfect agreement). Discordance between DIA and pathologists' consensus reads occurred in 5 PanNET cases which were upgraded from G1 to G2 by DIA due to contaminated Ki-67-stained inflammatory cells. CONCLUSIONS: DIA demonstrated excellent concordance with pathologists' assessments, with only minor grading discrepancies. However, the essential role of pathologists in confirming results is emphasized to enhance overall accuracy.

Concordance between pathologists and between specimen types in detection of HER2-low breast carcinoma by immunohistochemistry.

CONTEXT: Recent clinical trials indicate that HER2-targeted therapy may benefit HER2-low breast cancer patients including HER2 score 1+ or 2+ and no gene amplification. Concordance between pathologists and between core biopsy and surgical excision in establishing HER2-low status was evaluated. DESIGN: 57 patients with HER2 negative breast cancer (IHC 0, 1+, or 2+, no gene amplification) by core biopsy were included. Core biopsy and representative tumor from corresponding surgical excision was immunostained for HER2. Original HER2 IHC scores were interpreted using 2018 guidelines. Three pathologists independently interpreted again under 2023 guidelines. Kappa statistic evaluated agreement of HER2 IHC scores. RESULTS: Applying 2023 guidelines, HER2 IHC scores were concordant among study pathologists in 46 of 57 (81 %) core biopsy and 50 of 57 (88 %) surgical resections. Kappa statistics were 0.78 and 0.85 (substantial agreement), for inter-pathologist agreement of core biopsy and surgical resections under 2023 guidelines; 0.55 (moderate agreement) for agreement between first interpretation by 2018 guidelines and second interpretation by 2023 guidelines; and 0.13 (slight agreement) for agreement in HER2 consensus scores between outside core and surgical resection and 0.49 (moderate agreement) for inside core and surgical resection. Low HER2 expression was found in 28 of 57 (49 %) core biopsy and in 25 of 57 (44 %) surgical excisions. CONCLUSIONS: Interobserver agreement among study pathologists was good in core biopsy and surgical excisions, applying updated 2023 guidelines. Intratumoral heterogeneity in protein expression and preanalytical factors may result in variable identification of HER2-low status in core biopsy and surgical excision specimens.

Expression of CD25, mast cell markers and T-cell markers in eosinophilic esophagitis.

While eosinophilic esophagitis (EOE) is defined by histologic presence of eosinophils, a few studies have established the presence of mast cells in EOE and even shown their correlation with symptom persistence despite resolution of eosinophils. Expression of aberrant mast cell markers CD25 and CD2 have not been studied in EOE. This study quantifies the number of hotspot cells per high power field expressing CKIT/CD117, tryptase, CD25, CD2 and CD3 by immunohistochemical stains in endoscopic esophageal biopsies of the following three cohorts: (1) established and histologically confirmed EOE, (2) suspected EOE with biopsies negative for eosinophils, and (3) no history of or suspicion for EOE with histologically unremarkable biopsies. In this study, mast cells were highlighted by CKIT and tryptase in EOE, and not seen in other clinically mimicking cases. There were also significantly higher densities of CD25 and pan-T-cell marker staining in EOE cases. These findings suggest an inflammatory cellular milieu in EOE, beyond just eosinophils, that can be demonstrated by immunohistochemistry, and that invite further study into the role that these cells may play in EOE.

Assessing the relationship between tumor-infiltrating lymphocytes and PD-L1 expression in triple negative breast cancer: Identifying optimal TILs cut-off value for pathologic reporting.

BACKGROUND: Triple Negative Breast Cancer (TNBC) presents diagnostic complexities, particularly in evaluating Tumor-Infiltrating Lymphocytes (TILs) and Programmed Death-Ligand 1 (PD-L1) expression. This study aimed to identify optimal TILs percentage cut-offs predictive of PD-L1 expression and to investigate the relationship between TILs, PD-L1, and tertiary lymphoid structures (TLSs). METHOD: Analyzing 141 TNBC cases, we assessed TILs, PD-L1 expression (clones 22C3 and SP142), and TLS presence. RESULTS: We identified TILs cut-offs (<20 %, 20-60 %, ≥60 %) correlating with PD-L1 expression. TILs <20 % rarely express PD-L1 with either 22C3 or SP142 clones. TILs ≥60 % demonstrate PD-L1 expression across both clones. TILs within the 20-60 % range correlate with PD-L1 expression using the SP142 clone, but not 22C3. Evaluating TILs solely at the tumor edge led to inaccuracies, highlighting the need for overall assessment of TILs throughout the entire lesion. TLS presence correlated with higher TIL percentages and PD-L1 expression, particularly with SP142. Discrepancies between 22C3 and SP142 clones (15 % vs. 50 % positivity, respectively) underscored the variability in PD-L1 detection. CONCLUSION: This study identifies TILs cut-offs predictive of PD-L1 positivity, suggesting the need for institutions to tailor these thresholds based on the selected PD-L1 clone and treatment. Evaluating TILs solely at the tumor edge may overlook the complexity of tumor immune infiltration. While TLS presence correlates with higher PD-L1 expression, particularly with the SP142 clone, its exact predictive value for PD-L1 remains to be clarified. The SP142 clone exhibits higher positivity rates compared to 22C3.

Ependymomas of the spinal region in adults: Clinical and pathological features and MYCN expression levels in spinal ependymomas and myxopapillary ependymomas.

BACKGROUND: Ependymomas (EPNs) of the spinal region are a heterogeneous group of tumors that account for 17.6 % in adults. Four types have been recognized: subependymoma, spinal ependymoma (Sp-EPN), myxopapillary ependymoma (MPE), and Sp-EPN-MYCN amplified, each with distinct histopathological and molecular features. METHODS: This study investigated the clinical and pathological characteristics and MYCN expression levels of 35 Sp-EPN and MPE cases diagnosed at a tertiary university hospital over a decade-long period. RESULTS: Twenty-five cases were Sp-EPN and 10 cases were MPE, and were graded as WHO grade 2, except for 1 Sp-EPN case with grade 3 features. The most common symptoms were lower back pain and difficulty in walking. Radiology showed different tumor sizes and locations along the spinal cord, with MPEs exclusively in the lumbosacral region. Surgery was the main treatment, and gross total resection was achieved in all cases except for one. Immunohistochemistry showed low Ki-67 proliferation indices in all cases, and no MYCN expression. During follow-up, 3 (8.6 %) cases recurred and/or metastasized and 5 cases (14.3 %) died. No significant difference was found in disease-free survival or overall survival between Sp-EPN and MPE cases. However, 3 cases with grade 2 histology demonstrated recurrence and/or metastasis, despite the lack of MYCN expression. CONCLUSION: Our results underscore the multifactorial nature of tumor aggressiveness in EPNs of the spinal region. This study enhances our knowledge of the clinical and pathological features of Sp-EPNs and MPEs and highlights the need for better diagnostic and prognostic markers in these rare tumors.

A Comprehensive Study of Meningioma Biomineralization: Morphological, Crystallographic, and Immunohistochemical Aspects.

Biomineralization of brain tissues occurs both in normal and pathological conditions. Dura mater biomineralization is widespread and occurs in 1-72% of cases, depending on the patient's age and research method. The amount of biomineral deposits under the conditions of tumor growth in the meninges only increases, reaching 100% in the case of psammomatous meningiomas. Since calcifications are often found in the meninges, the problem of differential diagnosis with calcified meningiomas arises. A total of 30 samples of meningiomas with signs of biomineralization-dense structure, characteristic crunch, psammoma bodies (group I) and 30 samples of meningiomas without any signs of biomineralization were examined as controls (group II). To detect pathological biomineralization, the meningioma tissue was studied using the methods of macroscopic description, histology, histochemistry, and immunohistochemistry, scanning electron microscopy with microanalysis, and transmission electron microscopy. A significantly higher level of caspase3 and features of the expression of osteoblastic markers (a lower level of OPG expression and a higher level of the presence of RANKL in group I, the absence of fluctuations in the expression of SPARC) may indicate a dystrophic type of development of biomineral deposits in meningiomas.

The combined immunohistochemical expression of AMBRA1 and SQSTM1 identifies patients with poorly differentiated cutaneous squamous cell carcinoma at risk of metastasis: A proof of concept study.

BACKGROUND: Cutaneous squamous cell carcinoma (cSCC) incidence continues to increase globally with, as of yet, an unmet need for reliable prognostic biomarkers to identify patients at increased risk of metastasis. The aim of the present study was to test the prognostic potential of the combined immunohistochemical expression of the autophagy regulatory biomarkers, AMBRA1 and SQSTM1, to identify high-risk patient subsets. METHODS: A retrospective cohort of 68 formalin-fixed paraffin-embedded primary cSCCs with known 5-year metastatic outcomes were subjected to automated immunohistochemical staining for AMBRA1 and SQSTM1. Digital images of stained slides were annotated to define four regions of interest: the normal and peritumoral epidermis, the tumor mass, and the tumor growth front. H-score analysis was used to semi-quantify AMBRA1 or SQSTM1 expression in each region of interest using Aperio ImageScope software, with receiver operator characteristics and Kaplan-Meier analysis used to assess prognostic potential. RESULTS: The combined loss of expression of AMBRA1 in the tumor growth front and SQSTM1 in the peritumoral epidermis identified patients with poorly differentiated cSCCs at risk of metastasis (*p < 0.05). CONCLUSIONS: Collectively, these proof of concept data suggest loss of the combined expression of AMBRA1 in the cSCC growth front and SQSTM1 in the peritumoral epidermis as a putative prognostic biomarker for poorly differentiated cSCC.

Establishing guidelines for sentinel lymph node ultrastaging in endometrial cancer.

BACKGROUND: Many sentinel lymph node (SLN) ultrastaging protocols for endometrial cancer exist, but there is no consensus method. OBJECTIVE: This study aims to develop guidelines for size criteria in SLN evaluation for endometrial cancer, to determine whether a single cytokeratin AE1:AE3 immunohistochemical slide provides sufficient data for diagnosis, and to compare cost efficiency between current and limited ultrastaging protocols at a large tertiary care institution. METHODS: Our current SLN ultrastaging protocol consists of cutting two adjacent paraffin block sections at two levels (L1 and L2), 50 µm apart, with two slides at each level stained with hematoxylin and eosin and cytokeratin AE1:AE3 immunohistochemistry. We retrospectively reviewed digitized L1 and L2 slides of all positive ultrastaged SLNs from patients treated for endometrial cancer between January 2013 and January 2020. SLN diagnosis was defined by measuring the largest cluster of contiguous tumor cells in a single cross section: macrometastasis (>2.0 mm), micrometastasis (>0.2 to ≤2.0 mm or >200 cells), or isolated tumor cells (≤0.2 mm or ≤200 cells). Concordance between L1 and L2 results was evaluated. Cost efficiency between current (two immunohistochemical slides per block) and proposed limited (one immunohistochemical slide per block) protocols was compared. RESULTS: Digitized slides of 147 positive SLNs from 109 patients were reviewed; 4.1% of SLNs were reclassified based on refined size criteria. Complete concordance between L1 and L2 interpretations was seen in 91.8% of SLNs. A false-negative rate of 0%-0.9% in detecting micrometastasis and macrometastasis using a limited protocol was observed. Estimated charge-level savings of a limited protocol were 50% per patient. CONCLUSION: High diagnostic accuracy in SLN interpretation may be achieved using a limited ultrastaging protocol of one immunohistochemical slide per block and linear measurement of the largest cluster of contiguous tumor cells. Implementation of the proposed limited ultrastaging protocol may result in laboratory cost savings with minimal impact on health outcomes.