Breast cancer is one of the most common malignant tumors in women, with its incidence and mortality rates increasing annually. Early and accurate diagnosis and treatment of breast cancer patients are crucial for improving prognosis. Integrated positron emission tomography/magnetic resonance imaging (PET/MRI) as an emerging multimodal molecular imaging technology, combines the molecular metabolic imaging capabilities of PET with the high-resolution soft tissue imaging advantages of MRI. This allows for clearer identification of tumors and their relationships with surrounding tissues, holding significant clinical importance in the diagnosis and treatment of breast cancer. This article primarily reviews the applications and advancements of PET/MRI in the diagnosis, staging, molecular typing, and treatment monitoring of breast cancer.