Aim Fibroepithelial lesions (FELs) of the breast span a morphological continuum including lesions where distinction between cellular fibroadenoma (FA) and benign phyllodes tumour (PT) is difficult. The distinction is clinically important with FAs managed conservatively while equivocal lesions and PTs are managed with surgery. We sought to audit core biopsy diagnoses of equivocal FELs by digital pathology and to investigate whether digital point counting is useful in clarifying FEL diagnoses.
Method Scanned slide images from cores and subsequent excisions of 69 equivocal FELs were examined in a multicentre audit by eight pathologists to determine the agreement and accuracy of core needle biopsy (CNB) diagnoses and by digital point counting of stromal cellularity and expansion to determine if classification could be improved.
Results Interobserver variation was high on CNB with a unanimous diagnosis from all pathologists in only eight cases of FA, diagnoses of both FA and PT on the same CNB in 15 and a ‘weak’ mean kappa agreement between pathologists (k=0.36). ‘Moderate’ agreement was observed on CNBs among breast specialists (k=0.44) and on excision samples (k=0.49). Up to 23% of lesions confidently diagnosed as FA on CNB were PT on excision and up to 30% of lesions confidently diagnosed as PT on CNB were FA on excision. Digital point counting did not aid in the classification of FELs.
Conclusion Accurate and reproducible diagnosis of equivocal FELs is difficult, particularly on CNB, resulting in poor interobserver agreement and suboptimal accuracy. Given the diagnostic difficulty, and surgical implications, equivocal FELs should be reported in consultation with experienced breast pathologists as a small number of benign FAs can be selected out from equivocal lesions.
- breast pathology
- fibroepithelial lesions
- phyllodes tumour
- quality assurance
- digital pathology
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Handling editor Runjan Chetty.
Contributors BFD: audit coordinator, participated in audit, performed digital point counting, data collator, statistical analysis, principal author. AN, PHT, JT, BT: participated in audit, critically reviewed the manuscript. DT: supervised digital point counting, critically reviewed the manuscript. SU: performed preliminary audit, data collator, critically reviewed the manuscript. KM: statistical analyses, critically reviewed the manuscript. AMH: conceived and oversaw audit, participated in audit, critically reviewed the manuscript. RMS: conceived and oversaw the project, participated in audit, statistical analysis, critically reviewed the manuscript.
Competing interests PHT has patents titled ‘Exome Sequencing of Breast Fibroadenomas Reveals Highly Recurrent MED12 Exon 2 Somatic Mutations (Ref: TEA-P001WO)’, ‘Genomic Progression of Breast Fibroepithelial Tumors (Ref: TEA-P002WO)’ and ‘Multigene qPCR Assay Classifying Breast Fibroepithelial Lesions’. DT is an advisory board member of Sectra Medical and Leica and has research contracts with Leica, FFEI Life Science and Roche. DT receives no personal remuneration for any of these activities. Other authors have no competing interests to declare.
Ethics approval This is a diagnostic audit, a mandated requirement for ongoing quality assurance in pathology diagnostic laboratories in the UK. As such, ethics approval was not required. Audit approval was obtained from The Clinical Director of Pathology, St James’s University Hospital, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
Provenance and peer review Not commissioned; externally peer reviewed.