Breast cancer is the most common malignant tumor in women, which seriously threatens the physical and mental health of women worldwide. The existing detection methods have problems, such as large sample consumption,time-consuming sample preparation, expensive equipment, and low sensitivity. In order to solve these problems, this paper proposes a method for quickly detecting breast cancer using surface-functionalized terahertz metamaterial biosensors.The use of PIK3CA-modified sensors enhances the detection sensitivity and specificity of exosomes. Based on the red shift of the sensor absorption peak caused by exosomes, breast cancer patients can be distinguished from healthy controls. This study demonstrates that exosome detection is effective for the repeatable and non-invasive diagnosis of breast cancer patients. The terahertz metamaterial biosensor designed in this paper has high specificity, repeatability,and sensitivity, and has great potential for application in the development of modern diagnostic instruments.