Numerous clinicopathological features have been examined as predictive factors for adverse outcomes in patients with phyllodes tumor (PT) of the breast, but there are still no definitive predictive markers to guide management, despite the persistent risk of recurrence, even in benign disease. Whether Ki67 has prognostic value in PT remains uncertain. Therefore, a systematic review and meta‑analysis were performed to examine whether Ki67 is associated with adverse clinical outcomes, particularly recurrence, in patients with PT. The PubMed/MEDLINE, Web of Science, Scopus, Embase and Cochrane Library databases were searched from inception to July 2024. Study characteristics and outcomes (recurrence and overall survival) according to Ki67 status were extracted from each eligible study, and pooled log odds ratios (OR) with 95% CI were derived using a random‑effects model. A total of five studies comprising 280 cases were eligible for inclusion. The adverse outcome rate for the Ki67^high (Ki67 >10 or >11.2%) population was 28.7% (95% CI, 20.1‑38.6%), while the adverse outcome rate for the Ki67^low population was 9.4% (95% CI, 5.4‑13.5%). Ki67^high was associated with an increased odds of an adverse outcome [log OR, 1.26 (95% CI, 0.38‑2.15; P=0.005)] compared with a Ki67^low status. All five studies scored 8 points on the Newcastle‑Ottawa Scale, equivalent to ‘good’ quality according to Agency for Healthcare Research and Quality standards, and no significant publication bias was noted. This was the first meta‑analysis of the predictive value of Ki67 in PT of the breast. A relatively high Ki67 index (>10%) is associated with recurrence. It is timely to re‑evaluate the prognostic value of Ki67 in large retrospective cohorts with long follow‑up to firmly establish whether it could contribute to identifying patients at risk of recurrence, particularly those with histologically benign disease. Doing so could impact clinical practice by refining follow‑up recommendations based on quality evidence.

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