Classification of fibroepithelial lesions of the breast in core needle biopsy with implications for further management

Fibroepithelial lesions (FELs) of the breast constitute a heterogeneous group of biphasic tumours with variable morphology and behaviour. The classification of FELs is mainly based on a constellation of diagnostic criteria and intralesional heterogeneity is not uncommon. Therefore, reporting of FELs in a core needle biopsy (CNB) with limited tissue material can be challenging as not all the features may be represented for assessment. Distinction between classic fibroadenoma and representatively sampled phyllodes tumour is generally straightforward. However, cellular fibroadenoma, morphologically heterogeneous benign phyllodes tumour and myoid hamartoma can overlap histologically. Accurate grading of phyllodes tumour is also challenging on CNB and carries significant management implications. In this article, we provide an overview and propose a pragmatic approach to reporting FELs on CNB, particularly for lesions with overlapping features. Guidance using the UK/European 'B' classification of FELs, as well as free text descriptions of the various lesions, is also presented to help further management decision making.