ERBB2 and breast cancer: In an effort to deliver cytotoxic payloads more accurately in a package that has a lower molecular size than native antibodies, specific targets are engaged by peptide–drug conjugates using short peptides with high target affinity for tumour surface receptors or antigens, many of which are overexpressed in breast cancer subtypes including HER2, EGFR, integrins, or other tumour-related surface proteins.