Introduction: The immune system plays an important role in breast cancer. Triple-negative breast cancer has a high mutational burden and numerous neoantigens. This suggests that vaccination strategies are promising treatment options. Objective: The aim of this chapter is to discuss the rationale and evidence for mRNA vaccination strategies in breast cancer. Material and Methods: The basic principles of therapeutic vaccination with mRNA in breast cancer and the data available to date from clinical trials are presented. Results: Mutated neoantigens are an attractive target for vaccines. In particular, personalized mRNA vaccines against neoepitopes are promising and have shown efficacy in early studies in various malignant tumors such as breast cancer. Conclusion: mRNA vaccination has the potential to improve the survival of patients with breast cancer.