Ki-67 as a marker for differentiating borderline and benign phyllodes tumors of the breast: A meta-analysis and systematic review

Previously published studies raise the possibility of a link between breast phyllodes tumors (PT) grading and Ki-67 expression. In the current study, the authors conducted a literature review and meta-analysis to evaluate the association between the histological grades of PT and Ki-67 positivity, as well as the potential role of this immunomarker for the grading of PT. Observational studies grading PT and providing Ki-67 expression levels were retrieved from databases searches up to 11 August 2024, with 10 % or more of positive stromal cells being considered the cut-off point. A subgroup analysis included studies using the World Health Organization (WHO) criteria for PT grading. A total of 416 PT from 10 studies were included, with 25 % (106/416) showing increased Ki-67 expression. A significant association was found with increased Ki-67 expression in borderline PT compared to benign PT (OR 19.44; CI 3.11-121.74; P = 0.008; I² = 71 %). When comparing malignant and borderline tumors, a significant difference between the groups was observed (OR 7.87; 95 % CI 2.31-26.81; P < 0.01; I²: 49 %). However, in the subgroup of tumors using only the WHO classification, the association was non-significant (OR 5.50; 95 % CI 0.89-34.03; P = 0.07; I² = 64 %). Our meta-analysis showed an association between increased Ki-67 expression and borderline PT compared to benign tumors. The findings suggest Ki-67 may be a tool in the classification of PT, especially in histologically challenging cases.