Phyllodes tumour evidence gaps mapped from the 5th edition of the WHO classification of tumours of the breast

Aims: Breast phyllodes tumours (PTs) are a rare subset of fibroepithelial neoplasms categorised into benign, borderline, and malignant grades according to the World Health Organization (WHO) Classification of Tumours (WCTs). In this report, we developed an evidence gap map (EGM) based on the literature cited in the PT chapter of the 5th edition of the breast WCT in order to identify knowledge and research gaps in PT. Methods: A framework was first established where the dimensions of the EGM were defined as categories of tumour descriptors, tumour types, and evidence levels. Citations were collected into a Microsoft Excel form and imported into EPPI-reviewer to produce the EGM. Results: The EGM showed that the "Histopathology" and "Pathogenesis" sections contained the most citations, the majority being of low-level evidence. The highest number of citations considered of moderate-level evidence were found in the "Histopathology" section. There was no high-level evidence cited in this chapter. The "Localisation", "Aetiology", and "Staging" sections had the fewest citations. Conclusion: This EGM provides a visual representation of the cited literature in the PT chapter of the breast WCT, revealing the lack of high-level evidence citations. There is an uneven distribution of references, probably due to citation practices. Pockets of low-level evidence are highlighted, possibly related to referencing habits, lack of relevant research, or the belief that the information presented is standard accepted fact, without the need for specific citations. Future work needs to bridge evidence gaps and broaden citations beyond those in the latest WCT.