Objective:To investigate the expression level of serum ficolin-3 (FCN3) in breast cancer patients and its relationship with prognosis.Methods:A total of 145 patients with breast cancer (the breast cancer group) who were treated in Boao Evergrande International Hospital from February 2014 to February 2016 and 148 healthy women during the same period (the healthy control group) were selected. The level of FCN3 was detected by using enzyme-linked immunosorbent assay (ELISA); the serum carbohydrate antigen 153 (CA153) level of the two groups was detected by using automatic electrochemiluminescence immunoassay; the diagnostic value of serum FCN3 for breast cancer was evaluated by using receiver operating characteristic curve (ROC). The relationship between the level of serum FCN3 and the clinicopathological characteristics of breast cancer patients was analyzed. Kaplan-Meier method was used to analyze and compare the 3-year overall survival rate of breast cancer patients with different serum FCN3 levels.Results:Serum FCN3 level in breast cancer group was (14.1±3.4) μg/ml, which was higher than that in the healthy control group [(9.1±3.0) μg/ml], and the difference was statistically significant ( t = 13.644, P < 0.01). The serum CA153 level in breast cancer group was (36.3±15.2) U/ml, which was higher than that in the healthy control group [(16.8±6.9) U/ml], and the difference was statistically significant ( t = 14.397, P < 0.01). The area under the curve (AUC) of serum FCN3 and CA153 for the diagnosis of breast cancer was 0.894 and 0.720, respectively. The AUC of combined detection of serum FCN3 and CA153 for the diagnosis of breast cancer was 0.909, which was higher than that of CA153 alone ( Z = 2.050, P = 0.040), but compared with FCN3 alone, the difference was not statistically significant ( Z = 0.157, P = 0.875). Serum FCN3 level in stage Ⅲ breast cancer patients was higher than that in stage Ⅰ and Ⅱ patients, and serum FCN3 level in stage Ⅱ patients was higher than that in stage Ⅰ patients (all P < 0.05). The breast cancer patients with lymph node metastasis had higher serum FCN3 level compared with those patients without lymph node metastasis ( P < 0.05). The 3-year overall survival rate of breast cancer patients in the low-level FCN3 group (≤12.07 μg/ml) was higher than that in the high-level group (>12.07 μg/ml) ( P = 0.033). Conclusion:Serum FCN3 is up-regulated in breast cancer patients, which is expected to be a potential index for diagnosis and prognosis evaluation of breast cancer.