While early studies primarily cataloged protein abundance changes—such as EphA2 enrichment in gemcitabine-resistant PDAC (Fan et al., 2018), or mitochondrial Complex I upregulation in trastuzumab-resistant HER2+ breast cancer (Tapia et al., 2024)—contemporary proteomics has shifted focus to PTMs as direct mediators of resistance. The gene discussed is ERBB2; the disease is breast cancer.