Margin Adequacy in Phyllodes Tumors Revisited: Reappraisal of the Evidence Base and Knowledge Gaps

The optimal surgical margin for minimizing local recurrence (LR) and distant metastasis in phyllodes tumors (PTs) remains controversial. Despite multiple observational cohorts, variation among studies limits the interpretation of margin-outcome associations. We therefore performed a structured critical interpretative synthesis (CIS) to evaluate whether the current evidence supports specific margin thresholds. The CIS incorporated a systematic review, random-effects meta-analysis, an appraisal of existing meta-analyses and guidelines, and an expert interpretative analysis of 40 single-cohort studies from 2015 to 2025 evaluating surgical margin width and outcomes in PTs. Authors' recommendations regarding margin adequacy were extracted as interpretative "author conclusions." In parallel, LR and distant metastasis outcomes were pooled by tumor grade using random-effects models with prediction intervals. Final margin recommendations were derived by integrating CIS findings and multidisciplinary expert judgment. Current management guidelines do not recommend re-excision for positive or close margins in benign PTs. Contemporary guidelines are also concordant in advising negative margins for borderline and malignant PTs, although the specified margin width ranges from 1 to 10 mm. Within this range, no association has been established between increasing margin width and the risk of LR or malignant transformation upon LR. The estimated LR rates are 12.5% for borderline and 16.5% for malignant PTs. Malignant transformation on recurrence occurred in only 1% and 3% of all benign and borderline PTs, respectively. Approximately 14% of malignant PT metastasize, often without LR. Current heterogeneous evidence does not show lower recurrence with margins wider than a negative (≥1 mm) margin in PTs. For borderline and malignant PTs, a mandatory 10-mm threshold is insufficiently supported, as narrower negative margins may be adequate in selected cases. However, an optimal margin threshold cannot be defined from current data. These conclusions are practice-supporting rather than guideline-defining and reinforce the need for high-quality evidence to establish harmonized, grade-specific margin recommendations.