【Objective】 To explore the expression of PCDH9 loss in regulating cell cycle and promoting tumor progression. 【Methods】 The clinical records of 127 cases of prostate cancer treated during 2018 and 2023 were collected, including 87 paraffin tissue samples from the G4-5 group and 40 from the G1-3 group. The expressions of PCDH9, p53, Rb and STAT3 were detected with immunohistochemical staining, and the relationship between their expressions and clinicopathological characteristics was analyzed. 【Results】 The expression deletion rate of PCDH9 in prostate cancer tissues in G4-5 group (44.8% vs.7.5%) was significantly higher than that in G1-3 group (P<0.001). The positive expression rates of p53 and STAT3 were 34.5% and 89.7%, respectively, and the expression loss rate of Rb was 27.6% in G4-5 group. The expression loss rates of PCDH9 and Rb were associated with neuroendocrine-like histological morphology, nerve invasion and vascular invasion (P<0.05). In G4-5 group of prostate cancer, PCDH9 expression was positively correlated with the expressions of p53 (r=0.345, P<0.05), Rb (r=0.503, P<0.05) and STAT3 (r=0.224, P<0.05). 【Conclusion】 PCDH9 is prone to loss of expression in high-group prostate cancer tissues, especially in cases with neuroendocrine-like histological morphology, which may regulate the cell cycle through the STAT3 signaling pathway, thereby promoting tumor progression.