Correlations of morphological features and surgical management to clinical outcome in a multicentre study of 241 phyllodes tumours of the breast

Aims Phyllodes tumours (PTs) represent an unusual but complex group of breast lesions with a tendency to recur locally and less commonly metastasize. Their appearances can be difficult to discriminate from other fibroepithelial lesions on core biopsies, which may compromise their surgical management. The purpose of this study was to assess the preoperative diagnosis of PTs and to evaluate the impact of surgical management and of morphological features on their behaviour. Methods and results We combined datasets from three centres over two decades including core biopsies, excision specimens and follow-up. Core biopsy results were compared with final excision specimens. The relationships of surgical procedure and morphological features with local recurrence (LR) and metastasis was assessed. 241 PTs were studied. Core biopsy diagnosed possible or definite PT in 76% of cases. Malignant tumours were more likely to be larger, occurred at older age and were surgically more challenging, with difficulties in achieving negative margins. There were 12 cases (5%) which showed LR alone and another 6 cases (2.5%) had distant metastases. Morphological features associated with adverse outcome were the grade of PT, increased mitotic counts, necrosis, infiltrative margins, stromal atypia and heterologous components. Both LR and metastatic behaviour correlated with larger size and distance to margins. Conclusion Our results suggest that excision margins have a significant impact on LR of PT, while metastatic behaviour is influenced by tumour biology. We add to the evidence base about histological features of tumours which contribute to long-term outcomes of PTs.