PLK1 and bladder transitional cell carcinoma: Significant positive correlations were found between PLK1 expression and histologic grade (P = 0.005), recurrence (P < 0.001), and metastasis (P = 0.001) in urothelial carcinoma of the bladder, suggesting that PLK1 expression status is closely correlated with important histopathologic characteristics, including the grade and stage of bladder urothelial carcinoma54.