To address this issue, longitudinal multiomic profiling of HER2-low breast cancer is performed, including genomics, transcriptomics, proteomics, lactylomics, and phosphoproteomics, using 250 well-characterized samples, and identified three proteomic subtypes: PS1 (estrogen response signaling enriched), PS2 (angiogenesis enriched), and PS3 (proliferation enriched and HER2-high like). Here, ERBB2 is linked to breast cancer.