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The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, is the sixth version of the international standard for the classification of brain and spinal cord tumors. Building on the 2016 updated fourth edition and the work of the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy, the 2021 fifth edition introduces major changes that advance the role of molecular diagnostics in CNS tumor classification. At the same time, it remains wedded to other established approaches to tumor diagnosis such as histology and immunohistochemistry. In doing so, the fifth edition establishes some different approaches to both CNS tumor nomenclature and grading and it emphasizes the importance of integrated diagnoses and layered reports. New tumor types and subtypes are introduced, some based on novel diagnostic technologies such as DNA methylome profiling. The present review summarizes the major general changes in the 2021 fifth edition classification and the specific changes in each taxonomic category. It is hoped that this summary provides an overview to facilitate more in-depth exploration of the entire fifth edition of the WHO Classification of Tumors of the Central Nervous System.

cIMPACT-NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy) was established to evaluate and make practical recommendations on recent advances in the field of CNS tumor classification, particularly in light of the rapid progress in molecular insights into these neoplasms. For Round 2 of its deliberations, cIMPACT-NOW Working Committee 3 was reconstituted and convened in Utrecht, The Netherlands, for a meeting designed to review putative new CNS tumor types in advance of any future World Health Organization meeting on CNS tumor classification. In preparatory activities for the meeting and at the actual meeting, a list of possible entities was assembled and each type and subtype debated. Working Committee 3 recommended that a substantial number of newly recognized types and subtypes should be considered for inclusion in future CNS tumor classifications. In addition, the group endorsed a number of principles-relating to classification categories, approaches to classification, nomenclature, and grading-that the group hopes will also inform the future classification of CNS neoplasms.

* Context.--This article is based on a talk given by the lead author at the Eigth Annual Princeton Integrated Pathology Symposium: Breast Pathology, on Sunday, April 11, 2021. Objective.--To show how the World Health Organization (WHO) Classification of Tumours links to the requirements for quality assurance in breast pathology, including both immunohistochemistry and molecular pathology. Data Sources.--The WHO Classification of Tumours 5th edition Breast Tumours entries formed the basis of the talk, together with guidance published by the International Quality Network for Pathology. Conclusions.--The WHO Classification of Tumours provides a definitive set of international standards for tumor diagnosis contributed by experts, based on available clinical and research evidence. Techniques used in pathology need internal and external quality assurance to ensure accurate reports for patient management. doi: 10.5858/arpa.2021-0491-RA, The World Health Organization (WHO) Classification of Tumours now has 5 volumes published in the 5th edition, and will eventually encompass all tumors within a single classification (https://whobluebooks.iarc.who.int). The volume [...]

Aims: Ductal carcinoma in situ (DCIS) is recognised by the World Health Organisation (WHO) Classification of Tumours (WCT) as a non‐invasive neoplastic epithelial proliferation confined to the mammary ducts and lobules. This report categorises the references cited in the DCIS chapter of the 5th edition of the WCT (Breast Tumours) according to prevailing evidence levels for evidence‐based medicine and the Hierarchy of Evidence for Tumour Pathology (HETP), identifying potential gaps that can inform subsequent editions of the WCT for this tumour. Methods and results: We included all citations from the DCIS chapter of the WCT (Breast Tumours, 5th edition). Each citation was appraised according to its study design and evidence level. We developed our map of cited evidence, which is a graphical matrix of tumour type (column) and tumour descriptors (rows). Spheres were used to represent the evidence, with size and colour corresponding to their number and evidence level respectively. Thirty‐six publications were retrieved. The cited literature in the DCIS chapter comprised mainly case series and were regarded as low‐level. We found an unequal distribution of citations among tumour descriptors. 'Pathogenesis' and 'prognosis and prediction' contained the most references, while 'clinical features', 'aetiology' and 'diagnostic molecular pathology' had only a single citation each. 'Prognosis and prediction' had the greatest proportion of moderate‐ and high‐levels of evidence. Conclusion: Our findings align with the disposition for observational studies inherent in the field of pathology. Our map is a springboard for future efforts in mapping all available evidence on DCIS, potentially augmenting the editorial process and future editions of WCTs. [ABSTRACT FROM AUTHOR]

* Context.--There have been major advances in the understanding of melanoma since the last revision of the World Health Organization (WHO) classification in 2006. Objective.--To discuss development of the 9 distinct types of melanoma and distinguishing them by their epidemiology, clinical and histologic morphology, and genomic characteristics. Each melanoma subtype is placed at the end of an evolutionary pathway that is rooted in its respective precursor, wherever appropriate and feasible, based on currently known data. Each precursor has a variable risk of progression culminating in its fully evolved, invasive melanoma. Data Sources.--This review is based on the 'Melanocytic Tumours' section of the 4th edition of the WHO Classification of Skin Tumours, published in 2018. Conclusions.--Melanomas were divided into those etiologically related to sun exposure and those that are not, as determined by their mutational signatures, anatomic site, and epidemiology. Melanomas on the sun-exposed skin were further divided by the histopathologic degree of cumulative solar damage (CSD) of the surrounding skin, into low and high CSD, on the basis of degree of associated solar elastosis. Low-CSD melanomas include superficial spreading melanomas and high-CSD melanomas incorporate lentigo maligna and desmoplastic melanomas. The 'nonsolar' category includes acral melanomas, some melanomas in congenital nevi, melanomas in blue nevi, Spitz melanomas, mucosal melanomas, and uveal melanomas. The general term melanocytoma is proposed to encompass 'intermediate' tumors that have an increased (though still low) probability of disease progression to melanoma. (Arch Pathol Lab Med. 2020;144:500-522; doi: 10.5858/arpa.2019-0561-RA), This monograph represents a summary and discussion of a classification of melanoma that was developed for the WHO Classification of Skin Tumours, 4th edition, published in 2018. (1) As in [...]

The recently published WHO Reporting System for Pancreaticobiliary Cytopathology (World Health Organization [WHO] System) is an international approach to the standardized reporting of pancreaticobiliary cytopathology, updating the Papanicolaou Society of Cytopathology System for Reporting Pancreaticobiliary Cytology (PSC System). Significant changes were made to the categorization of benign neoplasms, intraductal neoplasms, mucinous cystic neoplasms, and malignant neoplasms considered low grade. Benign neoplasms, such as serous cystadenoma, categorized as Neoplastic: benign in the PSC system, are categorized as Benign/negative for malignancy in the WHO system. Pancreatic neuroendocrine tumor, solid‐pseudopapillary neoplasm, and gastrointestinal stromal tumor, categorized as Neoplastic: other in the PSC system, are categorized as Malignant in the WHO System in accord with their classification in the 5th edition WHO Classification of Digestive System Tumours (2019). The two new categories of Pancreaticobiliary Neoplasm Low‐risk/grade and Pancreaticobiliary Neoplasm High‐risk/grade are mostly limited to intraductal neoplasms and mucinous cystic neoplasms. Low‐risk/grade lesions are mucinous cysts, with or without low‐grade epithelial atypia. High‐risk/grade lesions contain neoplastic epithelium with high‐grade epithelial atypia. Correlation with clinical, imaging, and ancillary studies remains a key tenet. The sections for each entity are written to highlight key cytopathological features and cytopathological differential diagnoses with the pathologist working in low resource setting in mind. Each section also includes the most pertinent ancillary studies useful for the differential diagnosis. Sample reports are provided for each category. Finally, the book provides a separate section with risk of malignancy and management recommendations for each category to facilitate decision‐making for clinicians. The recently published World Health Organization System for reporting pancreatobiliary cytopathology is an update to the Papanicolaou System for reporting pancreatobiliary cytopathology, building on the key concepts and changing the categorization of some neoplasms to better reflect their biological behavior. This review summarizes the key points and organization. [ABSTRACT FROM AUTHOR]