The covalent immunochemotherapeutics, gemcitabine-(C4-amide)-[anti-EGFR] and gemcitabine-(C4-amide)-[anti-HER2/neu] each have potent selective “targeted” anti-neoplastic cytotoxic properties against chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3). The gene discussed is ERBB2; the disease is breast adenocarcinoma.