PLK1 and breast cancer: A meta-analysis of breast cancer patients revealed that high PLK1 expression was correlated with large tumor size (>2 cm) (P < 0.001) in 1779 breast cancer patients, higher tumor grade (P < 0.001) in 1989 patients and, lymph node metastasis (P = 0.001) in 1975 patients50, suggesting that high PLK1 expression indicates poor clinical outcomes in breast cancer patients.