Abstract
The newly published World Health Organization (WHO) Classification of Tumours of the breast features significant changes compared to earlier editions. In this review, we outline the major changes in this important reference source for those diagnosing tumours, or engaged in cancer research, and describe the significant changes. For breast cancer, the overview acknowledges the treatment-relevant subtypes of invasive carcinoma (based on ER and HER2 status) and new data is added to support the differences in pathogenesis, treatment response and prognosis of these clinically relevant groupings. The WHO Classification of Tumours is increasingly evidence-based, with a clear update cycle, improved quality of illustrations, as well as content, led by an editorial board comprising pathologists, but increasingly incorporating input from other disciplines. The advent of the new website allows the use of whole slide images, and hyperlinks to evidence or external bodies that produce guidance on staging or reporting.
Highlights
The classification of breast tumours continues to evolve, with the integration of new knowledge from research rapidly being translated into clinical practice
According to the proposed consensus terminology, well-differentiated neuroendocrine tumours (NETs) broadly correspond to grade 1 and grade 2 tumours, whereas poorly differentiated neuroendocrine carcinomas (NECs) are typified by small-cell and large-cell carcinoma
Many breast tumours that show varying degrees of neuroendocrine differentiation belong to recognised entities, such as hypercellular mucinous carcinoma and solid papillary carcinoma of both in-situ and invasive types
Summary
The classification of breast tumours continues to evolve, with the integration of new knowledge from research rapidly being translated into clinical practice. In this volume of the World Health Organization (WHO) classification of tumours series’ fifth edition, which is an update of the fourth-edition breast tumours volume published in 2012,1 the descriptions of breast tumours follow the familiar systematic approach of previous volumes, with the content organised in sequence from benign epithelial proliferations and precursors, through benign neoplasms, to in-situ and invasive breast cancer, followed by mesenchymal and haematolymphoid neoplasms, tumours of the male breast, and genetic tumour syndromes. Information on epidemiology, imaging, clinical features, grading, staging, molecular testing for hormone receptors and ERBB2 (HER2), post-therapy effects, core needle biopsy and fine-needle aspiration considerations, molecular pathology and genomics is presented in the general overview that introduces the sections on invasive breast carcinoma (IBC), rather than in the first chapter as in the previous edition. Essential and desirable diagnostic criteria are included, to reinforce key histopathological clues
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