Abstract: Objective To study the relationship between the expression level of PLK1 in castration-resistant prostate cancer (CRPC) tissues, and its relationship with pathological features. Methods Forty-four CRPC specimens including 28 samples from patients with prostate adenocarcinoma, 14 samples from patients with neuroendocrine prostate cancer (NEPC) and 2 samples from patients with other types of prostate cancer, and 10 normal prostatic hyperplasia specimens were collected from January 2010 to September 2016 in the Second Hospital of Tianjin Medical University. The expression levels of PLK1 in these tissues were detected by S- P immunohistochemistry. The relationship between PLK1 expression and pathologic factors was discussed. Results The positive expression of PLK1 was located in cytoplasm of carcinoma cells, and no express of PLK1 was found in benign prostatic hyperplasia tissues. The expression levels of PLK1 showed no significantly differences between different groups of age, local tumor invasion and regional nodal status, and the level of prostate-specific antigen (PSA, P＞0.05). The expression level of PLK1 in patients with Gleason score >8 was higher than that in patients with Gleason score≤8. The PLK1 expression level was positively correlated with Gleason score (rs=0.441， P＜ 0.05). Conclusion PLK1 protein is over-expressed in CRPC tissues, which can reflect the proliferation and differentiation of cancer cells and may be a potential marker of CRPC.

Key words: prostatic neoplasms, immunohistochemistry, castration- resistant prostate cancer, Polo- like kinase 1, clinical characteristic