The DNA Structure-Specific Endonuclease MUS81 Mediates DNA Sensor STING-Dependent Host Rejection of Prostate Cancer Cells.

Self-DNA is present in the cytosol of many cancer cells and can promote effective immune rejection of tumor cells, but the mechanisms leading to the presence of cytosolic DNA are unknown. Here, we report that the cleavage of genomic DNA by DNA structure-specific endonuclease MUS81 and PARP-dependent DNA repair pathways leads to the accumulation of cytosolic DNA in prostate cancer cells. The number of nuclear MUS81 foci and the amount of cytosolic dsDNA increased in tandem from hyperplasia to clinical stage II prostate cancers and decreased at stage III. Cytosolic DNA generated by MUS81 stimulated DNA sensor STING-dependent type I interferon (IFN) expression and promoted phagocytic and T cell responses, resulting in type I and II IFN-mediated rejection of prostate tumor cells via mechanisms that partly depended on macrophages. Our results demonstrate that the tumor suppressor MUS81 alerts the immune system to the presence of transformed host cells.

The Prognostic Value of CD39 as a Marker of Tumor-Specific T Cells in Triple-Negative Breast Cancer in Asian Women.

Triple-negative breast cancer (TNBC) has a poor prognosis with limited therapeutic options available for affected patients. Efforts are ongoing to identify surrogate markers for tumor-specific CD8+ T cells that can predict the response to immune checkpoint inhibitor (ICI) therapies, such as programmed cell death protein 1 or programmed cell death ligand-1 blockade. We have previously identified tumor-specific CD39+CD8+ T cells in non-small cell lung cancer that might help predict patient responses to programmed cell death protein 1 or programmed cell death ligand-1 blockade. Based on this finding, we conducted a comparative interrogation of TNBC in an Asian cohort to evaluate the potential of CD39 as a surrogate marker of tumor-specific CD8+ T cells. Using ICI-treated TNBC mouse models (n = 24), flow cytometric analyses of peripheral blood mononuclear cells and tumor-infiltrating lymphocytes revealed that >99% of tumor-specific CD8+ T cells also expressed CD39. To investigate the relationship between CD39+CD8+ T-cell density and CD39 expression with disease prognosis, we performed multiplex immunohistochemistry staining on treatment-naive human TNBC tissues (n = 315). We saw that the proportion of CD39+CD8+ T cells in human TNBC tumors correlated with improved overall survival, as did the densities of other CD39+ immune cell infiltrates, such as CD39+CD68+ macrophages. Finally, increased CD39 expression on CD8+ T cells was also found to predict the response to ICI therapy (pembrolizumab) in a separate cohort of 11 TNBC patients. These findings support the potential of CD39+CD8+ T-cell density as a prognostic factor in Asian TNBC patients.

A Preliminary Investigation into Search and Matching for Tumor Discrimination in World Health Organization Breast Taxonomy Using Deep Networks.

Breast cancer is one of the most common cancers affecting women worldwide. It includes a group of malignant neoplasms with a variety of biological, clinical, and histopathologic characteristics. There are more than 35 different histologic forms of breast lesions that can be classified and diagnosed histologically according to cell morphology, growth, and architecture patterns. Recently, deep learning, in the field of artificial intelligence, has drawn a lot of attention for the computerized representation of medical images. Searchable digital atlases can provide pathologists with patch-matching tools, allowing them to search among evidently diagnosed and treated archival cases, a technology that may be regarded as computational second opinion. In this study, we indexed and analyzed the World Health Organization breast taxonomy (Classification of Tumors fifth ed.) spanning 35 tumor types. We visualized all tumor types using deep features extracted from a state-of-the-art deep-learning model, pretrained on millions of diagnostic histopathology images from the Cancer Genome Atlas repository. Furthermore, we tested the concept of a digital "atlas" as a reference for search and matching with rare test cases. The patch similarity search within the World Health Organization breast taxonomy data reached >88% accuracy when validating through "majority vote" and >91% accuracy when validating using top n tumor types. These results show for the first time that complex relationships among common and rare breast lesions can be investigated using an indexed digital archive.

A New Hierarchy of Research Evidence for Tumor Pathology: A Delphi Study to Define Levels of Evidence in Tumor Pathology.

The hierarchy of evidence is a fundamental concept in evidence-based medicine, but existing models can be challenging to apply in laboratory-based health care disciplines, such as pathology, where the types of evidence and contexts are significantly different from interventional medicine. This project aimed to define a comprehensive and complementary framework of new levels of evidence for evaluating research in tumor pathology-introducing a novel Hierarchy of Research Evidence for Tumor Pathology collaboratively designed by pathologists with help from epidemiologists, public health professionals, oncologists, and scientists, specifically tailored for use by pathologists-and to aid in the production of the World Health Organization Classification of Tumors (WCT) evidence gap maps. To achieve this, we adopted a modified Delphi approach, encompassing iterative online surveys, expert oversight, and external peer review, to establish the criteria for evidence in tumor pathology, determine the optimal structure for the new hierarchy, and ascertain the levels of confidence for each type of evidence. Over a span of 4 months and 3 survey rounds, we collected 1104 survey responses, culminating in a 3-day hybrid meeting in 2023, where a new hierarchy was unanimously agreed upon. The hierarchy is organized into 5 research theme groupings closely aligned with the subheadings of the WCT, and it consists of 5 levels of evidence-level P1 representing evidence types that merit the greatest level of confidence and level P5 reflecting the greatest risk of bias. For the first time, an international collaboration of pathology experts, supported by the International Agency for Research on Cancer, has successfully united to establish a standardized approach for evaluating evidence in tumor pathology. We intend to implement this novel Hierarchy of Research Evidence for Tumor Pathology to map the available evidence, thereby enriching and informing the WCT effectively.

Moving Forward on Tumor Pathology Research Reporting: A Guide for Pathologists From the World Health Organization Classification of Tumors Living Evidence Gap Map by Tumour Type Group.

Evidence-based medicine (EBM) can be an unfamiliar territory for those working in tumor pathology research, and there is a great deal of uncertainty about how to undertake an EBM approach to planning and reporting histopathology-based studies. In this article, reviewed and endorsed by the Word Health Organization International Agency for Research on Cancer's International Collaboration for Cancer Classification and Research, we aim to help pathologists and researchers understand the basics of planning an evidence-based tumor pathology research study, as well as our recommendations on how to report the findings from these. We introduce some basic EBM concepts, a framework for research questions, and thoughts on study design and emphasize the concept of reporting standards. There are many study-specific reporting guidelines available, and we provide an overview of these. However, existing reporting guidelines perhaps do not always fit tumor pathology research papers, and hence, here, we collate the key reporting data set together into one generic checklist that we think will simplify the task for pathologists. The article aims to complement our recent hierarchy of evidence for tumor pathology and glossary of evidence (study) types in tumor pathology. Together, these articles should help any researcher get to grips with the basics of EBM for planning and publishing research in tumor pathology, as well as encourage an improved standard of the reports available to us all in the literature.

Mucinous cystadenocarcinoma of the breast harbours TRPS1 expressions and PIK3CA alterations.

AIMS: Breast mucinous cystadenocarcinoma (BMCA) is a rare tumour recently recognised as a distinct entity by the World Health Organisation Tumour Classification Series. BMCA is a triple-negative tumour that lacks specific immunohistochemical markers; therefore, distinguishing it from mimickers such as ovarian and pancreatic cystadenocarcinomas requires careful clinicopathological correlation. Due to its rarity, little is known about the molecular alterations that underlie BMCA. METHODS AND RESULTS: In this study, we used immunohistochemical staining methods to investigate TRPS1 (trichorhinophalangeal syndrome type 1) expression in BMCA and compare it to expression in ovarian and pancreatic mucinous cystadenocarcinomas. We also collected tumour samples from three BMCA patients for molecular analysis by MALDI-TOF mass spectrometry, real-time polymerase chain reaction, whole exome sequencing and fluorescence in-situ hybridisation. TRPS1 immunoreactivity was found only in BMCA tumour cells and not in the ovarian and pancreatic counterparts. One of the three BMCA tumours also showed a PIK3CA hot-spot mutation, which was confirmed by whole genome next-generation sequencing (NGS). No KRAS, NRAS, BRAF or AKT mutations were found. CONCLUSIONS: To our knowledge, this is the first demonstration of TRPS1 expression in BMCA patients and the first identification of a PIK3CA hotspot mutation in these tumours. These findings provide insights into the molecular mechanisms underlying BMCA tumorigenesis and suggest a potential drug target for this rare and poorly understood cancer.

Human epidermal growth factor receptor 2 (HER2) status in breast cancer: practice points and challenges.

Human epidermal growth factor receptor 2 (HER2)-enriched breast cancer benefits significantly from anti-HER2 targeted therapies. This highlights the critical need for precise HER2 immunohistochemistry (IHC) interpretation serving as a triage tool for selecting patients for anti-HER2 regimens. Recently, the emerging eligibility of patients with HER2-low breast cancers for a novel HER2-targeted antibody-drug conjugate (T-DXd) adds challenges to HER2 IHC scoring interpretation, notably in the 0-1+ range, which shows high interobserver and interlaboratory staining platform variability. In this review, we navigate evolving challenges and suggest practical recommendations for HER2 IHC interpretation.

A dedicated structured data set for reporting of invasive carcinoma of the breast in the setting of neoadjuvant therapy: recommendations from the International Collaboration on Cancer Reporting (ICCR).

AIMS: The International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter-)national pathology and cancer organisations, is an initiative aimed at providing a unified international approach to reporting cancer. ICCR recently published new data sets for the reporting of invasive breast carcinoma, surgically removed lymph nodes for breast tumours and ductal carcinoma in situ, variants of lobular carcinoma in situ and low-grade lesions. The data set in this paper addresses the neoadjuvant setting. The aim is to promote high-quality, standardised reporting of tumour response and residual disease after neoadjuvant treatment that can be used for subsequent management decisions for each patient. METHODS: The ICCR convened expert panels of breast pathologists with a representative surgeon and oncologist to critically review and discuss current evidence. Feedback from the international public consultation was critical in the development of this data set. RESULTS: The expert panel concluded that a dedicated data set was required for reporting of breast specimens post-neoadjuvant therapy with inclusion of data elements specific to the neoadjuvant setting as core or non-core elements. This data set proposes a practical approach for handling and reporting breast resection specimens following neoadjuvant therapy. The comments for each data element clarify terminology, discuss available evidence and highlight areas with limited evidence that need further study. This data set overlaps with, and should be used in conjunction with, the data sets for the reporting of invasive breast carcinoma and surgically removed lymph nodes from patients with breast tumours, as appropriate. Key issues specific to the neoadjuvant setting are included in this paper. The entire data set is freely available on the ICCR website. CONCLUSIONS: High-quality, standardised reporting of tumour response and residual disease after neoadjuvant treatment are critical for subsequent management decisions for each patient.

Peroxiredoxin 3 regulates breast cancer progression via ERK-mediated MMP-1 expression.

Peroxiredoxin 3 (PRDX3), a mitochondrial hydrogen peroxide scavenger, is known to be upregulated during tumorigenesis and cancer progression. In this study, we provide evidence for the first time that PRDX3 could regulate cellular signaling pathways associated with Matrix Metalloproteinase-1 (MMP-1) expression and activity in breast cancer progression. We show that shRNA-mediated gene silencing of PRDX3 inhibits cell migration and invasion in two triple-negative breast cancer cell lines. Reciprocal experiments show that PRDX3 overexpression promotes invasion and migration of the cancer cells, processes which are important in the metastatic cascade. Notably, this phenomenon may be attributed to the activation of MMP-1, which is observed to be upregulated by PRDX3 in the breast cancer cells. Moreover, immunohistochemical staining of breast cancer tissues revealed a positive correlation between PRDX3 and MMP-1 expression in both epithelial and stromal parts of the tissues. Further pathway reporter array and luciferase assay demonstrated that activation of ERK signaling is responsible for the transcriptional activation of MMP-1 in PRDX3-overexpressed cells. These findings suggest that PRDX3 could mediate cancer spread via ERK-mediated activation of MMP-1. Targeted inhibition of ERK signaling may be able to inhibit tumor metastasis in triple-negative breast cancer.

Outcomes in Nonmetastatic Hormone Receptor-Positive HER2-Negative Pure Mucinous Breast Cancer: A Multicenter Cohort Study.

BACKGROUND: Although considered a favorable subtype, pure mucinous breast cancer (PMBC) can recur, and evidence for adjuvant therapy is limited. We aimed to compare outcomes of nonmetastatic PMBC with invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) to address these uncertainties. METHODS: Individual patient-level data from 6 centers on stage I-III hormone receptor-positive and HER2-negative PMBC, IDC, and ILC were used to analyze recurrence-free interval (RFI), recurrence-free survival (RFS), and overall survival (OS), and to identify prognostic factors for PMBC. RESULTS: Data from 20,684 IDC cases, 1,475 ILC cases, and 943 PMBC cases were used. Median follow-up was 6.6 years. Five-year RFI, RFS, and OS for PMBC were 96.1%, 94.9%, and 98.1%, respectively. On multivariable Cox regression, PMBC demonstrated superior RFI (hazard ratio [HR], 0.59; 95% CI, 0.43-0.80), RFS (HR, 0.70; 95% CI, 0.56-0.89), and OS (HR, 0.71; 95% CI, 0.53-0.96) compared with IDC. ILC showed comparable outcomes to IDC. Fewer than half (48.7%) of recurrences in PMBC were distant, which was a lower rate than for IDC (67.3%) and ILC (80.6%). In contrast to RFI, RFS events were driven more by non-breast cancer deaths in older patients. Significant prognostic factors for RFI among PMBC included positive lymph node(s) (HR, 2.42; 95% CI, 1.08-5.40), radiotherapy (HR, 0.44; 95% CI, 0.23-0.85), and endocrine therapy (HR, 0.25; 95% CI, 0.09-0.70). No differential chemotherapy associations with outcomes were detected across PMBC subgroups by nodal stage, tumor size, and age. A separate SEER database analysis also did not find any association of improved survival with adjuvant chemotherapy in these subgroups. CONCLUSIONS: Compared with IDC, PMBC demonstrated superior RFI, RFS, and OS. Lymph node negativity, adjuvant radiotherapy, and endocrine therapy were associated with superior RFI. Adjuvant chemotherapy was not associated with better outcomes.

Epithelial Carcinomas Arising within Phyllodes Tumours of the Breast: A Review of Their Pathological Characteristics.

Epithelial proliferation is a common feature of phyllodes tumours (PTs), but epithelial malignancy is rare. This review seeks to further our understanding of epithelial malignancy within PTs by analysing their histopathological characteristics in previously reported cases and providing an overview of studies on their pathological features. PubMed and DeepDyve were searched for case reports, case series, and literature reviews of in situ and invasive carcinoma within PTs. Only cases where the carcinoma was within the PT were included. Cases of synchronous carcinoma in the ipsilateral or contralateral breast were excluded. Ninety-eight cases of in situ or invasive carcinoma within a PT were identified. Across the grades of PTs, there was a similar proportion of invasive carcinomas compared to in situ lesions. Malignant PT correlates with a higher likelihood of epithelial malignancy, and molecular studies support a possible causal pathophysiological relationship. This higher likelihood may suggest interactions between malignant stroma and the transforming epithelium that could potentially play a significant role in the phenomenon, which remains to be elucidated. Encasement within a PT likely improves the prognosis of breast carcinoma due to earlier detection. The presence of carcinoma within a malignant PT has uncertain prognostic implications. Thorough sampling of all PTs is recommended for appropriate prognostication and management.

Challenges and clinical relevance of modern breast pathology reporting - your questions answered.

BACKGROUND: Breast pathology reporting, especially for breast cancer, has evolved through the years, from terse succinct diagnostic conclusions with scant histological details to the current comprehensive reporting guidelines issued by major pathology colleges and bodies, including the International Collaboration on Cancer Reporting. Pathology elements included in reporting guidelines are evidence based and contribute significantly to individualised and personalised patient management. SUMMARY: This article is based on the lively interactive question and answer session that followed the breast pathology segment in the symposium jointly organised by the British Association of Urological Pathology, British Association of Gynaecological Pathologists, British Society of Gastroenterology and the Association of Breast Pathology, in November 2022, titled 'Personalised histopathology reporting for personalised medicine'. KEY MESSAGES: The breast pathology session emphasized the clinical utility of breast pathology data items, incorporating a case-based approach by highlighting the relevance of pathology information in various clinical scenarios. This review included clinico-pathological discussion points on florid lobular carcinoma in situ (LCIS), atypical apocrine adenosis, post-neoadjuvant chemotherapy reporting, atypical ductal hyperplasia (ADH) presenting at the margin, flat epithelial atypia (FEA) vs columnar cell change (CCC), papilloma on core needle biopsy (CNB), margin status, mucocele-like lesion, total duct excision/microdochectomy specimen, and anterior and nipple margins in skin-sparing mastectomy. Effective communication and regular involvement of pathologists in breast multidisciplinary tumour boards are crucial.

Prognostic Value of Tumor Budding in Urothelial Carcinoma: A Meta-Analysis and Systematic Review.

Recently, tumor budding (TB) has been suggested as a strong prognostic marker in urinary tract urothelial carcinoma (UC). The aim of this systematic review is to test the prognostic value of TB in UC by a meta-analysis of previously published studies. We systematically reviewed the literature related to TB by using the databases of Scopus, PubMed, and Web of Science. The search was limited to publications in the English language up to July 2022. There were 790 patients from 7 retrospective studies in which TB has been evaluated in UC. Two authors independently extracted the results from eligible studies. The meta-analysis of eligible studies revealed that TB is a significant prognosticator for progression-free survival in UC, with a hazard ratio (HR) of 3.51 (95% CI, 1.86-6.62; P < .001) in univariate analysis and a HR of 2.78 (95% CI, 1.57-4.93; P < .001) in multivariate analysis; a significant prognosticator for overall survival and cancer-specific survival in UC, with a HR of 3.07 (95% CI, 2.04-4.64; P < .001) and a HR of 2.18 (95% CI, 1.11-4.29; P = .02) respectively in univariate analysis. Our findings confirm that UC with a high TB count is at a high risk of progress. TB could be considered as an element in pathology reports and future oncologic staging systems.

Abnormal lactate metabolism is linked to albuminuria and kidney injury in diabetic nephropathy.

Diabetic nephropathy (DN) is characterized by abnormal kidney energy metabolism, but its causes and contributions to DN pathogenesis are not clear. To examine this issue, we carried out targeted metabolomics profiling in a mouse model of DN that develops kidney disease resembling the human disorder. We found a distinct profile of increased lactate levels and impaired energy metabolism in kidneys of mice with DN, and treatment with an angiotensin-receptor blocker (ARB) reduced albuminuria, attenuated kidney pathology and corrected many metabolic abnormalities, restoring levels of lactate toward normal while increasing kidney ATP content. We also found enhanced expression of lactate dehydrogenase isoforms in DN. Expression of both the LdhA and LdhB isoforms were significantly increased in kidneys of mice, and treatment with ARB significantly reduced their expression. Single-cell sequencing studies showed specific up-regulation of LdhA in the proximal tubule, along with enhanced expression of oxidative stress pathways. There was a significant correlation between albuminuria and lactate in mice, and also in a Southeast Asian patient cohort consisting of individuals with type 2 diabetes and impaired kidney function. In the individuals with diabetes, this association was independent of ARB and angiotensin-converting enzyme inhibitor use. Furthermore, urinary lactate levels predicted the clinical outcomes of doubling of serum creatinine or development of kidney failure, and there was a significant correlation between urinary lactate levels and biomarkers of tubular injury and epithelial stress. Thus, we suggest that kidney metabolic disruptions leading to enhanced generation of lactate contribute to the pathogenesis of DN and increased urinary lactate levels may be a potential biomarker for risk of kidney disease progression.

Early Triple-Negative Breast Cancers in a Singapore Cohort Exhibit High PIK3CA Mutation Rates Associated With Low PD-L1 Expression.

Mutations in the PI3K pathway, particularly PIK3CA, were reported to be intimately associated with triple-negative breast cancer (TNBC) progression and the development of treatment resistance. We profiled PIK3CA and other genes on 166 early-stage TNBC tumors from Singapore for comparison to publicly available TNBC cohorts. These tumors were profiled transcriptionally using a NanoString panel of immune genes and multiplex immunohistochemistry, then manually scored for PD-L1-positivity using 2 clinically relevant clones, SP142 and 22C3. We discovered a higher rate of PIK3CA mutations in our TNBC cohort than in non-Asian cohorts, along with TP53, BRCA1, PTPN11, and MAP3K1 alterations. PIK3CA mutations did not affect overall or recurrence-free survival, and when compared with PIK3CAWT tumors, there were no differences in immune infiltration. Using 2 clinically approved antibodies, PIK3CAmut tumors were associated with PD-L1 negativity. Analysis of comutation frequencies further revealed that PIK3CA mutations tended to be accompanied by MAP kinase pathway mutation. The mechanism and impact of PIK3CA alterations on the TNBC tumor immune microenvironment and PD-L1 positivity warrant further study.

An international unified approach to reporting and grading invasive breast cancer. An overview of the International Collaboration on Cancer Reporting (ICCR) initiative.

Standardised reporting of breast cancer key pathology data has become the norm in some parts of the world, but are based on national or regional guidelines that differ in certain aspects, resulting in divergent reporting practices and a lack of comparability of data internationally. The International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter-)national pathology and cancer organizations, have recently produced a new international dataset for the pathology reporting of breast cancer, including resection specimens with invasive cancer and ductal carcinoma in situ (DCIS) of the breast. This initiative aims at providing an international unified approach to reporting cancer. The guidance was prepared by an international expert panel consisting of experienced breast pathologists, a surgeon, and an oncologist. The dataset includes core (essential) and noncore (optional) data items based on a critical review and discussion of current evidence. Commentary is provided for each data item to explain the rationale for selection, its clinical relevance, and to highlight potential areas of disagreement or lack of evidence, in which case a consensus position was formulated. The process concludes with international public consultation, before ratification and publication on the free open access ICCR website, with a synoptic reporting guide. The key aim is to promote high-quality, standardised pathology reporting that can be used worldwide. Histological grade, tumour size, and oestrogen receptor status are used in this article to illustrate this process and the detail provided to support its inclusion.

Tertiary lymphoid structures in breast ductal carcinoma in situ correlate with adverse pathological parameters.

AIMS: To investigate tertiary lymphoid structures (TLSs) in ductal carcinoma in situ (DCIS) of the breast and their correlation with pathological features, immune cell markers and clinical outcomes. METHODS AND RESULTS: Morphological identification of TLSs in 198 DCIS cases incorporated B and T cell zones with high endothelial venules. TLS positivity was defined as ≥ 1 TLSs in lesional areas, while TLS area percentage was divided into two categories: low (TLSs < 5%) and high (TLSs ≥ 5%). Previously reported biomarkers included ER, PR, HER2, CD68, CD163, CD4, CD8 and PD-L1. TLSs were observed in 24.7% (49 of 198) of cases, with a mean diameter of 0.44 mm (median = 0.4 mm, range = 0.12-1.43 mm). TLSs were significantly associated with higher nuclear grade, presence of necrosis, hormone receptor negativity/HER2 positivity, triple negativity, tumour infiltrating lymphocytes (TILs) and immune related biomarkers such as FOXP3, CD163, CD4 and CD4/CD8 ratio (all P < 0.05). There were no significant associations between TLSs and recurrence, but a combination of TLSshigh with FOXP3+ , CD4high , CD4/CD8 ratiohigh and CD68high individually, compared with all other combinations, disclosed significantly poorer disease-free survival (DFS) for ipsilateral invasive recurrence (IIR) on both Kaplan-Meier and multivariable Cox regression analyses (all P < 0.05). CONCLUSIONS: TLSs in DCIS were associated with unfavourable prognostic features, TILs and immune cell markers in our study. TLSshigh /FoxP3+ , TLSshigh /CD4high , TLSshigh /(CD4/CD8) ratiohigh and TLSshigh /CD68high were independent factors for poorer DFS for IIR. Further exploration of the pathological significance of TLSs may provide a clinical basis for their recognition as an important structure and functional unit in the tumour immune microenvironment.

Survey of recurrent diagnostic challenges in breast phyllodes tumours.

BACKGROUND: Breast phyllodes tumours (PTs) are graded as benign, borderline, or malignant by analysis of multiple histological features. PT grading is often inconsistent, likely due to variation in the weighting of grading criteria by pathologists. DESIGN: The hierarchy of use of diagnostic criteria was identified using a 20-question survey. RESULTS: In all, 213 pathologists from 29 countries responded. 54% reported 10-50 PT cases per year. Criteria considered key to PT diagnosis were: increased stromal cellularity (84.3%), stromal overgrowth (76.6%), increased stromal mitoses (67.8%), stromal atypia (61.5%), stromal fronding (59.0%), periductal stromal condensation (58.0%), irregular tumour borders (46.3%), and/or lesional heterogeneity (33.7%). The importance of grading parameters were: mitotic activity (55.5%), stromal overgrowth (54.0%), stromal atypia (51.9%), increased stromal cellularity (41.7%), and nature of the tumour border (38.9%). 49% would diagnose malignant PT without a full array of adverse features. 89% used the term "cellular fibroepithelial lesion (FEL)" for difficult cases; 45% would diagnose an FEL with stromal fronding (but lacking other PT features) as fibroadenoma (FA), 35% FEL, and 17% PT. 59% deemed clinico-radiological findings diagnostically significant; 68% considered age (≥40 years) important in determining if an FEL was a FA or PT. In FELs from young patients, increased stromal cellularity (83%), fronding (52%), and mitoses (41%) were more common. 34% regarded differentiating cellular FA from PT as a specific challenge; 54% had issues assigning a borderline PT grade. CONCLUSION: Criteria for grading PT lie on a spectrum, leading to interpretive variability. The survey highlights the criteria most used by pathologists, which do not completely align with WHO recommendations.

Phyllodes tumour evidence gaps mapped from the 5th edition of the WHO classification of tumours of the breast.

AIMS: Breast phyllodes tumours (PTs) are a rare subset of fibroepithelial neoplasms categorised into benign, borderline, and malignant grades according to the World Health Organization (WHO) Classification of Tumours (WCTs). In this report, we developed an evidence gap map (EGM) based on the literature cited in the PT chapter of the 5th edition of the breast WCT in order to identify knowledge and research gaps in PT. METHODS: A framework was first established where the dimensions of the EGM were defined as categories of tumour descriptors, tumour types, and evidence levels. Citations were collected into a Microsoft Excel form and imported into EPPI-reviewer to produce the EGM. RESULTS: The EGM showed that the "Histopathology" and "Pathogenesis" sections contained the most citations, the majority being of low-level evidence. The highest number of citations considered of moderate-level evidence were found in the "Histopathology" section. There was no high-level evidence cited in this chapter. The "Localisation", "Aetiology", and "Staging" sections had the fewest citations. CONCLUSION: This EGM provides a visual representation of the cited literature in the PT chapter of the breast WCT, revealing the lack of high-level evidence citations. There is an uneven distribution of references, probably due to citation practices. Pockets of low-level evidence are highlighted, possibly related to referencing habits, lack of relevant research, or the belief that the information presented is standard accepted fact, without the need for specific citations. Future work needs to bridge evidence gaps and broaden citations beyond those in the latest WCT.

Giant juvenile fibroadenomas with and without prominent pseudoangiomatous stromal hyperplasia (PASH)-like change: clinicopathological and molecular characteristics.

AIMS: Juvenile fibroadenomas (JFA) are biphasic fibroepithelial lesions (FEL) usually occurring in adolescent female patients. Giant (G) JFA, like other FEL, may exhibit prominent pseudoangiomatous stromal hyperplasia (PASH)-like change. We sought to determine clinicopathological and molecular characteristics of GJFA with and without PASH. METHODS AND RESULTS: Archives were searched for cases of GJFA (1985-2020). All were stained for androgen receptor (AR), beta-catenin, CD34 and progesterone receptor (PR). Cases were sequenced using a custom 16-gene panel - MED12 (exons 1 and 2), TERT promoter (-124C>T and -146Ctable>T), SETD2, KMT2D, RARA (exons 5-9), FLNA, NF1, PIK3CA (exons 10, 11 and 21), EGFR, RB1, BCOR, TP53, PTEN, ERBB4, IGF1R and MAP3K1. Twenty-seven GJFA from 21 female patients aged 10.1-25.2 years were identified. Size ranged from 5.2 to 21 cm. Two patients had multiple, bilateral and later recurrent GJFA. Thirteen (48%) cases showed prominent PASH-like stroma. All were positive for stromal CD34, negative for AR and beta-catenin and one case showed focal PR expression. Sequencing showed MAP3K1 and SETD2 mutations in 17 samples, with KMT2D, TP53 and BCOR aberrations in 10 (45%), 10 (45%) and seven (32%) cases, respectively. Tumours with a PASH-like pattern had higher prevalence of SETD2 (P = 0.004) and TP53 (P = 0.029) mutations, while those without PASH had more RB1 mutations (P = 0.043). MED12 mutation was identified in one case. TERT promoter mutation was observed in four (18%), including two recurrences. CONCLUSIONS: Gene mutations along more advanced phases of the proposed FEL pathogenetic pathway in GJFA are unusual, and suggest a mechanism for more aggressive growth in these tumours.