Keynote Lecture: KN02 UPDATE ON WHO BREAST CLASSIFICATION - 2 YEARS ON.

The 4 edition of the WHO classification of Tumours of the Breast was published in 2012, as a separate volume from the gynae book. The editors and the international panel of breast pathologists have attempted to produce a consensus document that will help to standardize classification worldwide. In addition to microscopic criteria that define tumour types, there is incorporation of relevant updated molecular information.Many of the diagnostic problems in clinical practice reside in the B3 category, which comprises a heterogeneous group of proliferations that include atypical ductal hyperplasia (ADH), lobular neoplasia (ALH/LCIS), columnar cell lesions (CCL) and flat epithelial atypia (FEA), radial scar (RS/CSL), phyllodes tumours, papillary lesions, mucinous lesions and spindle cell proliferations. In clinical practice, the rate of B3-biopsies ranges from 3-10%.In this lecture, I will cover some of the diagnostic issues that have been discussed since the publication of the 4 edition. They centre on this group of lesions which form a significant component of consult practice throughput the world, suggesting that the diagnostic criteria and classification systems are still far from robust.