Do alternative classification systems improve prognostication in phyllodes tumours of the breast? A comparative clinicopathological study.

Abstract

Aims: Phyllodes tumours of the breast (PTs) present complex histological features that challenge classification. The WHO 5th Edition (2019) defines malignancy based on five simultaneous criteria, which may under-recognize tumours with metastatic potential. Alternative diagnostic systems have been proposed, but comparative data are limited.

Methods and results: We reviewed 62 PTs diagnosed as borderline or malignant between 2015 and 2025. Histological features were re-evaluated, and tumours were classified according to WHO (2019), Tan et al. (2025), and the Refined Criteria (2023). After exclusion of 4 reclassified benign cases, 58 tumours (42 borderline, 16 malignant) were analysed. The mean patient age was 45 years, and the mean tumour size was 6.7 cm. After a median follow-up of 31.7 months, 6 borderline PTs recurred locally without metastasis. Among malignant PTs, seven developed distant metastases, with two disease-related deaths. High stromal mitotic activity (≥30/10 HPF, P = 0.005) and malignant heterologous elements (P < 0.001) were independently associated with metastasis. Tan et al.'s classification showed 97% concordance with WHO 2019, whereas the Refined Criteria reclassified 52% of borderline tumours as malignant; none of the reclassified tumours developed distant metastases during the available follow-up.

Conclusions: In this cohort, high stromal mitotic activity and malignant heterologous elements were the strongest predictors of recurrence in PTs. Tan et al.'s classification system demonstrated close concordance with the WHO (2019) criteria, whereas the Refined Criteria classified a substantially greater proportion of tumours as malignant without improving prognostic discrimination during the available follow-up period. Comprehensive tumour sampling remains essential for accurate classification and reliable prognostic assessment of PTs of the breast.