Objective:To investigate the relationship between serum Mir-137 and Mir-140 levels and clinicopathological features of breast cancer patients and recurrence and metastasis after postoperative chemotherapy with adriamycin + cyclophosphamide + docetaxel (ACT) .Methods:Female breast cancer patients who received chemotherapy of ACT regimen after modified radical mastectomy or breast-conserving radical mastectomy in Tongcheng People’s Hospital from Jan. 2017 to Apr. 2019 were included as research objects, and 60 healthy subjects who underwent physical examination in our hospital during the same period were included as healthy control group. Two ml of fasting peripheral venous blood was extracted from all patients before surgery and 1 week after the end of chemotherapy, and the relative expression levels of Mir-137 and Mir-140 in serum were determined by quantitative real-time polymerase linked reaction. Clinicopathological data were collected, including age, menopausal status, pathological type, TNM stage, estrogen receptor (ER) status, progesterone receptor, PR and human epidermal growth factor receptor-2 (HER2) status. All breast cancer patients were followed up for 3 years after surgery, and postoperative recurrence, distant metastasis and death time were recorded according to medical records and follow-up results.Results:The relative expression of Mir-137 in breast cancer patients was 0.89±0.15, significantly lower than that in healthy controls (1.34±0.21) ( t=4.985, P<0.001) . The relative expression of Mir-140 in breast cancer patients was 0.83±0.14, significantly lower than that in healthy controls (1.18±0.17) ( t=4.245, P<0.001) . Serum Mir-137 level was correlated with TNM stage, ER status and HER2 status in breast cancer patients ( t=2.56, 2.06, 2.24, P=0.003, 0.007, 0.004) , and serum Mir-140 level was correlated with TNM stage and HER2 status in breast cancer patients ( t=1.954, 2.114, P=0.008, 0.006) . After chemotherapy, the relative expression levels of serum Mir-137 and serum Mir-140 in breast cancer patients were 1.05±0.16 and 0.97±0.18, respectively, significantly higher than those before surgery ( t=2.689 and 3.051, P=0.004 and 0.002, respectively) . A total of 17 patients developed recurrence or distant metastasis within 3 years, and the 3-year progression-free survival rate was 71.67% (43/60) . The mir-137 level of patients with recurrent metastasis was 0.74±0.14, significantly lower than that of patients without recurrent metastasis (0.94±0.13) , the difference was statistically significant ( t=4.149, P<0.001) . The mir-140 level of patients with recurrent metastasis was 0.73±0.10, which was significantly lower than that of patients without recurrent metastasis (0.87±0.13) , the difference was statistically significant ( t=3.634, P<0.001) . ROC curve analysis showed that the sensitivity and specificity of serum Mir-137 expression level in predicting recurrence and metastasis of breast cancer patients were 82.4% and 79.1%, respectively. The sensitivity and specificity of serum Mir-140 expression level in predicting recurrence and metastasis of breast cancer patients were 82.4% and 69.8%, respectively. Kaplan-meier survival curve analysis showed that the 3-year progression-free survival rate of patients with low Mir-137 level was significantly lower than that of patients with high Mir-137 level ( P=0.025) . There was no significant difference in 3-year progression-free survival between patients with low mir-140 level and those with high Mir-140 level ( P=0.282) . Conclusion:Serum Mir-137 and Mir-140 levels are related to clinicopathological features and the efficacy of ACT chemotherapy after operation, which can be used as indicators to evaluate the disease and prognosis.