Objective:To investigate the correlation of PELP1/MNAR expression with expressions of estrogen receptor (ER), Ki-67, human epidermal growth factor receptor 2 (HER2) and PIK3CA gene mutation.Methods:A total of 80 paraffin-embedded tissue specimens of primary invasive breast cancer patients in the Fifth People's Hospital of Datong in Shanxi Province from January 2008 to December 2018 were collected. The expression of PELP1/MNAR was examined by immunohistochemistry EliVision tow-step method. The polymerase chain reaction (PCR)-Sanger sequencing method was used to detect the mutation of PIK3CA gene. The expressions of PELP1/MNAR among patients with different expression status of ER, Ki-67, HER2 and with or without PIK3CA gene mutation were compared, and the correlations between each index and the expression of PELP1/MNAR were analyzed.Results:The high expression rates of PELP1/MNAR protein in patients with ER-positive [86.1% (31/36) vs. 59.1% (26/44)], Ki-67 high expression [100.0% (13/13) vs. 65.7% (44/67)], HER2-positive [81.0% (34/42) vs. 60.5% (23/38)] were high, and the differences were statistically significant (all P<0.05). There was no significant difference in the high expression rate of PELP1/MNAR protein between patients with mutant and wild-type PIK3CA [60.0% (12/20) vs. 75.0% (45/60), P = 0.199]. The expression of PELP1/MNAR was negatively correlated with the expression level of ER ( r = -0.195, P < 0.05), positively correlated with the expression level of Ki-67 ( r = 0.198, P < 0.05), positively correlated with the expression level of HER2 ( r = 0.225, P < 0.05), and negatively correlated with lymph node metastasis ( r = -0.269, P < 0.05). Conclusions:The expression of PELP1/MNAR in invasive breast cancer is negatively correlated with the expression level of ER, and positively correlated with the expression level of Ki-67 and HER2. There is no correlation between PELP1/MNAR expression and PIK3CA gene mutation, and the two may play their own role in the PI3K-AKT-mTOR regulatory pathway of breast cancer.