Purpose: Diagnosis of breast preneoplastic and neoplastic lesions is di cult due to their similar morphology in breast biopsy specimens. To diagnose these lesions, pathologists perform immunohistochemical analysis and consult with expert breast pathologists. These additional examinations are time-consuming and expensive. Arti cial intelligence (AI)-based image analysis has recently improved, and may help in ordinal pathological diagnosis. Here, we showed the signi cance of machine learning-based image analysis of breast preneoplastic and neoplastic lesions for facilitating high-throughput diagnosis.Methods: Images were obtained from normal mammary glands, hyperplastic lesions, preneoplastic lesions and neoplastic lesions, such as usual ductal hyperplasia (UDH), columnar cell lesion (CCL), ductal carcinoma in situ (DCIS), and DCIS with comedo necrosis (comedo DCIS) in breast biopsy specimens.The original enhanced convoluted neural network (CNN) system was used for analyzing the pathological images.Results: The AI-based image analysis provided the following area under the curve values (AUC): normal lesion vs. DCIS, 0.9902; DCIS vs. comedo DCIS, 0.9942; normal lesion vs. CCL, 0.9786; and UDH vs. DCIS, 1.000. Multiple comparison analysis showed precision and recall scores similar to those of single comparison analysis. Based on the Gradient-weighted Class Activation Mapping (Grad-CAM) used to visualize the important regions re ecting the result of CNN analysis, the ratio of stromal tissue in the whole weighted area was signi cantly higher in UDH and CCL than that in DCIS.Conclusions: These analyses may provide a more accurate and rapid pathological diagnosis of patients. Moreover, Grad-CAM identi es uncharted important histological characteristics for newer pathological ndings and targets of research for understanding diseases.