Abstract: Background and purpose: Prospero-related homeobox 1 (PROX1), a member of the homeodomain transcription factor family, is involved in the development and progression of a variety of malignant tumors, and is closely related to tumor cell proliferation, differentiation, apoptosis, migration and invasion. This study explored the expression of PROX1 in breast cancer tissues and its correlation with prognosis. Methods: A total of 85 patients with breast cancer underwent elective surgery, and complete data were collected from Mar. 2011 to Mar. 2013. Immunohistochemical staining was used to detect the protein level of PROX1 in breast cancer and adjacent tissues. All patients were followed up, and 4 patients were lost during follow-up. Follow-up deadline was Mar. 31, 2018. Kaplan-Meier method and Log-rank test were used for survival analysis. Cox proportional hazards regression model was used to analyze the prognostic factors of breast cancer. Results: The positive rate of PROX1 protein was 71.76% in breast cancer tissues and 28.57% in adjacent tissues (χ²=32.600, P<0.001). The expression of PROX1 protein in breast cancer tissues was significantly different in the degree of differentiation, TNM stage, estrogen receptor (ER), Ki-67 labeling index and lymph node metastasis compared with adjacent tissues (P<0.05). Kaplan-Meier survival analysis showed that the mean survival time of the PROX1 positive expression group was (36.73±2.73) months, and that of the PROX1 negative expression group was (56.36±2.13) months. The Log-rank test  howed the difference in mean survival time was statistically significant between the two groups (χ²=11.803, P=0.001). The Cox proportional hazards regression model showed that the degree of differentiation, TNM stage, lymph node metastasis and PROX1 protein expression were risk factors for the prognosis of breast cancer patients (P<0.05). Conclusion: PROX1 is highly expressed in breast cancer tissues, and is closely related to the occurrence and progression of breast cancer and prognosis of patients. It is a risk factor affecting the prognosis of patients.

Key words: Breast cancer, Prospero-related homeobox 1, Prognosis, Cox proportional hazards regression model