Enhanced levels of anti-neoplastic cytotoxicity for gemcitabine-(C4-amide)-[anti-EGFR] or epirubicin-(C3-amide)-[anti-HER2/neu] against chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3) and potentially other chemotherapeutic-resistant cancer populations can be attributed to covalent bonding of the chemotherapeutic moieties to a delivery platform that has a much larger molecular weight (e.g. IgG MW = 150,000 Da -vs- gemcitabine MW = 263.198 Da). The gene discussed is ERBB2; the disease is cancer.