MS2M: Multi-Granularity Self-Supervised Second-Order Multiple Instance Learning for Breast Cancer Pathology Image

Combining Big Data and deep learning can analyze large-scale breast cancer pathology images for auxiliary diagnosis. Furthermore, Whole Slide Images (WSIs) of breast cancer pathology offer detailed tissue feature information, which supports the accurate identification of malignant lesions. Current approaches combine Self-Supervised Learning (SSL) and Multiple Instance Learning (MIL) for WSI analysis, aiming to address the issues of billion-level pixels in a single WSI and the lack of precise annotations. However, pseudo-labels produced by SSL frequently lack accuracy, and MIL fails to effectively integrate global information at the WSI level, resulting in performance bottlenecks. This paper proposes the Multi-granularity Self-supervised Second-order MIL (MS2M) to tackle these issues. MS2M first achieves instance-level fine-grained feature learning through multi-granularity SSL and optimizes instance-level representations using bag-level labels within the MIL framework. Then, the transformer captures long-range dependencies between instances. When combined with second-order (covariance) pooling, it also captures high-order relational information. This process generates a robust bag-level representation. MS2M achieves accuracies of 0.9845 and 0.9719 on the CAMELYON16 and private breast cancer WSI datasets, respectively, outperforming existing methods.