Prognostic Significance of Three-Tiered World Health Organization Classification of Phyllodes Tumor and Correlation to Singapore General Hospital Nomogram

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Abstract
Objectives: Phyllodes tumors (PTs) are categorized by the World Health Organization (WHO) as benign, borderline, and malignant. Singapore General Hospital (SGH) nomogram is a recurrence risk assessment tool for PT, which uses cytologic atypia, mitosis, stromal overgrowth, and the surgical margin status. We studied the prognostic significance of WHO classification and its correlation to the SGH nomogram. Methods: We identified 270 consecutive cases of PT (195 benign, 49 borderline, 26 malignant). Follow-up was available on 246 cases (mean follow-up of 51 months). Results: The recurrence rates were 2% (4 of 176) for benign, 4% (2 of 46) for borderline, and 25% (6 of 24) for malignant (log-rank test P < .0001 for recurrence-free survival). Only five patients with malignant PT experienced distant recurrence. Stromal overgrowth was an independent predictor of recurrence-free survival on multivariable analysis. The mean nomogram scores for benign, borderline, and malignant PT were 20, 20.3, and 32, respectively. The higher than expected score for benign PT was due to positive margins in 39% of cases. Conclusions: The WHO three-tiered classification of PT is prognostic. Despite positive margin status, most benign PTs do not recur. Other features of the nomogram help in determining recurrence but are also used for WHO classification.

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