Molecular pathology of phyllodes tumours of the breast—much more than <i>MED12</i>

Phyllodes tumours of the breast present challenges in their diagnosis, classification and management. Further understanding of the molecular changes underpinning these tumours may lead to more precise classification and potential treatment options. Similar to fibroadenomas, MED12 is the most frequently mutated gene in phyllodes tumour. However, in addition, there is a spectrum of molecular alterations from benign to malignant phyllodes tumours with increasing genomic complexity, high level copy number alterations and aberrations of cancer driver genes in malignant phyllodes tumours. This review summarizes the molecular pathology of phyllodes tumours, the use of these data in developing a model of phyllodes tumour pathogenesis, and how molecular pathology might be applied to aid diagnosis and guide treatment in this rare tumour type.