Abstract: Background and purpose: Polo-like kinase 4 (PLK4) is mainly involved in regulation of the replication process of centrosome. Overexpression of PLK4 can induce the enlargement of the centrosome, cause instability of the chromosomes, and enhance tumor invasiveness. The purpose of this research was to investigate the expression of PLK4 in human colorectal cancer (CRC), and evaluate its clinicopathological significance. Methods: Fresh tissues of 19 cases of CRC and adjacent normal tissues were collected, and paraffin specimens of 129 cases of CRC tissues and adjacent tissues were collected. PLK4 mRNA expression was measured from 19 cases of CRC and corresponding normal tissues by real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR). Immunohistochemical staining was performed to detect the PLK4 expression in 129 cases of CRC and corresponding normal tissues. The association of the PLK4 expression with clinicopathological parameters and prognostic significance was evaluated. Results: The level of PLK4 mRNA expression in CRC tissues was significant higher than in the corresponding normal tissues (P<0.01). Immunohistochemical staining showed PLK4 protein was localized in cytoplasm and part of nucleus in CRC cells. In 129 cases of CRC, low expression of PLK4 protein was found in 62 cases whereas PLK4 protein was highly expressed in 67 cases. PLK4 protein expression in CRC was significantly higher than that in adjacent tissues (P<0.01). There was a correlation of PLK4 expression with higher histological grading (P=0.001 1), higher incidence of lymph node metastasis (P<0.000 1), distant metastasis (P=0.035 8) and TNM staging (P<0.000 1). Kaplan-Meier survival curves showed that the median survival time was 27 months in PLK4 protein low expression group, and 12 months in PLK4 protein high expression group. Log-rank test results showed that high PLK4 expression was found to be a detrimental prognostic factor measured by overall survival (OS) (P<0.000 1). Multivariate COX proportional hazards model analysis showed that PLK4 high expression was not an independent prognostic factor for CRC (P=0.176). Conclusion: PLK4 was highly expressed in CRC tissues, and was associated with poor CRC differentiation, lymph node metastasis, distant metastasis and TNM stage. The high expression of PLK4 suggests that CRC has poor prognosis, but it is not an independent prognostic factor.

Key words: Polo-like kinases 4, Colorectal cancer, Metastasis, Prognosis