Objective:To investigate the value of dual-layer detector spectral CT in preoperative evaluation of immunohistochemical expression levels in breast cancer patients.Methods:The clinical, pathological and imaging data of breast cancer patients who received preoperative spectral CT chest scan in Affiliated Hospital of Southwest Medical University from October 2020 to January 2021 were retrospectively analyzed. A total of 70 patients were divided into positive or negative estrogen receptor (ER) group, positive or negative progesterone receptor (PR) group, positive or negative human epithelial growth factor receptor 2 (HER2) group, and positive or negative Ki-67 group according to the immunohistochemistry. Philips workstation and Special Diagnostic Suite software were used for processing and analysis. The CT value and iodine concentration value (IC) of the lesion and the effective atomic number (Z eff) of the lesion in the arterial and venous phases were measured, and the standardized CT value (NCT), standardized iodine concentration value (NIC), slope (K) of the keV-CT value curve in the arterial and venous phases as well as the CT difference and the IC difference in the arteriovenous phase were calculated. Independent sample t test was used to compare the differences in spectral parameters between patients with positive and negative immunohistochemical parameters, and ROC curve was used to analyze the efficacy of spectral parameters in the differential diagnosis of positive and negative different immunohistochemical parameters. Results:Z eff, NIC, K value, CT value, IC value of arterial and venous phase and NCT value of venous phase in negative ER group were higher than those in positive ER group, the difference was statistically significant ( P<0.05). Z eff, NIC, K value, IC, CT difference in arteriovenous phase and IC difference in arteriovenous phase in positive HER2 group were higher than those in negative HER2 patients, the difference was statistically significant (P<0.05). The arterial K value in positive Ki-67 group was higher than that in negative Ki-67 group, the difference was statistically significant ( P<0.05). Taking arterial phase K value of 1.22 as the diagnostic threshold, it had the highest diagnostic efficiency in differential diagnosis of ER positivity versus negativity (area under curve of 0.791, sensitivity of 84.00%, specificity of 65.00%). Taking the arteriovenous phase IC difference of 0.47 mg/ml as the diagnostic threshold, it had the highest performance in differential diagnosis of HER2 positivity versus negativity (area under curve of 0.736, sensitivity of 76.32%, specificity of 65.62%). Conclusion:Dual-layer detector spectral CT has certain diagnostic value for the immunohistochemical expression of breast cancer patients, which can provide reference for clinical diagnosis and treatment.