We have developed the MMTV-R26Met mouse model, which exclusively generates TNBC and recapitulates key features of the human disease in an immunocompetent setting. In this study, we provide a proteomics characterization of MMTV-R26Met-derived tumors. This integrative approach reveals distinct tumor clusters that reflect patient-like heterogeneity and provides a valuable framework for TNBC stratification and therapeutic development.