Phyllodes tumours of the breast: a 20-year institutional series with emphasis on criteria for malignancy.

BACKGROUND

Although histological criteria underpin current classification, accurate risk stratification, particularly for borderline and malignant tumours, remains challenging.

METHODS

We analysed a 20-year institutional series of phyllodes tumours (PTs), integrating clinicopathological data with long-term clinical outcomes. Histological features were extracted from original pathology reports, with slide re-review where archival material was available.

RESULTS

Among 111 PTs, 80% were benign, 11% borderline and 9% malignant. The follow-up ranged from 0 to 20 years, with 11.3, 10.3 and 7.6 years for benign, borderline and malignant PT, respectively. Most patients underwent local excision; mastectomy was performed in 22% of malignant PT. Final positive margins were identified in 18% of benign, 8% of borderline and none of the malignant tumours. Adjuvant radiotherapy was administered in 18% of borderline and 67% of malignant PT. Local recurrence occurred in 3%, 11% and 22% of benign, borderline and malignant tumours, respectively. Distant metastases were observed exclusively in malignant PTs (33%, 3/9 cases), two of which were preceded by local recurrence. Notably, two of the three metastatic malignant PTs showed either ≤10 mitoses/10 high-power field or <marked stromal atypia and lack of stromal overgrowth, which are required for diagnosis of malignant PT per WHO 5th edition recommendation. The low event rate precluded robust multivariable analysis.

CONCLUSION

Our results highlight the biological heterogeneity of malignant PTs and the limitations of rigid histological thresholds. These findings underscore the need for collaborative, multi-institutional prospective studies with standardised tumour sampling and reporting and molecular correlation to refine clinically meaningful risk stratification in PT.