New aspects in the classification of epithelial tumors of the mammary gland

Abstract

The classification of breast tumors continues to evolve, with new knowledge from research being applied in practice. The new volume of the World Health Organization (WHO) Classification from 2019 is an update of the fourth edition of breast tumors, published in 2012. The descriptions of breast diseases follow the familiar systematic approach of previous volumes. The content is organized in the following sequence: from benign epithelial proliferations and precursors, through benign neoplasms, to in situ and invasive breast cancer, followed by fibroepithelial and nipple tumors, mesenchymal and hematolymphoid neoplasms, tumors of the male breast and genetic tumor syndromes. A brief introduction precedes the contents of each chapter of the book to provide an overview of the nosological units involved and to highlight key changes in the current classification. New histological variants of mammary carcinoma have been introduced, others have completely disappeared, some of them have been moved to another category of tumors, and still others have been transformed from a special subtype carcinoma into a growth pattern of invasive breast carcinoma of no special type. Neuroendocrine tumors are consistent with the same tumors located in other organs and systems, and the criteria for both microinvasion and mixed forms of breast cancer are indicated. The classification of breast tumors is a dynamic process that uses many sources of up-to-date information that have emerged since the publication of the latest WHO update. Some of the innovations could be integrated very successfully into the algorithms of digital pathology, which would improve the diagnostic accuracy and thus would lead to optimization of the choice of therapeutic strategies and estimation of the correct prognosis.