Aberrant expression of polo-like kinase 4 in renal cell carcinoma: Association with clinicopathological characteristics and long-term survival

Polo-like kinase 4 (PLK4) promotes tumorigenesis and is associated with the prognosis of several solid tumors, while its clinical role in patients with renal cell carcinoma (RCC) remains unidentified. The present study aimed to analyze the association of PLK4 with clinicopathological characteristics and long-term prognosis in patients with RCC. The present study detected PLK4 protein and mRNA expression using immunohistochemical and reverse transcription-quantitative PCR assays in 120 patients with RCC. Disease-free survival (DFS) and overall survival (OS) time were calculated based on a median follow-up duration of 6.9 years (range, 1.2-9.9 years). PLK4 protein expression was elevated in tumor tissues compared with adjacent tissues (P<0.001). Upregulation of PLK4 protein was associated with increased T stage (P=0.023), N stage (P=0.014) and TNM stage (P=0.007). Additionally, elevated tumor PLK4 protein expression exhibited an associating trend (without statistical significance) with reduced DFS rate (P=0.066) and was associated with decreased OS rate (P=0.036). However, univariate Cox's regression analysis indicated that high PLK4 protein expression (compared with low PLK4 protein expression) was associated with reduced OS rate (P=0.040) but not with PFS rate (P=0.070). Following adjustment by multivariate Cox's regression analysis, PLK4 protein expression was associated with neither DFS nor OS rate (both P>0.050). Additionally, PLK4 mRNA expression was further detected in some patients (for which fresh specimens frozen in liquid nitrogen were available) to validate the aforementioned observations, and the expression was elevated in tumor tissues compared with adjacent tissues. Furthermore, increased PLK4 mRNA expression was associated with tumor size ≥7 cm, high TNM stage and reduced DFS rate (all P<0.050). PLK4 possesses a certain clinical utility in monitoring the clinical stage of patients with RCC, while its prognostic value requires further validation.