A Molecular and Morphological Deep-Dive Into Metaplastic Breast Cancers

Metaplastic breast cancers (MBC) are relatively rare but account for significant global breast cancer mortality. Typically presenting without oestrogen and progesterone receptors or HER2 expression, these triple negative breast cancers are the archetypal ‘stem cell-like’ tumours that show a variety of metaplastic elements, including squamous, spindle, and chondroid. Given the vast heterogeneity in MBC by definition, large cohort studies are needed to draw conclusions. Together with our consortium colleagues, a cohort of 347 MBC was established, and a detailed morphological assessment made in an effort to understand the clinical relevance of the current diagnostic guidelines. Biomarker expression was investigated, and whole exome sequencing was performed. Herein, we provide an overview and contextualisation of the study.