Anti-neoplastic cytotoxicity potencies for gemcitabine-(C4-amide)-[anti-HER2/neu] at the end of a 182-hour incubation period were similar to gemcitabine following a 72-hour incubation period in populations of chemotherapeutic-resistant mammary adenocarcinoma (SKBr-3). The gene discussed is ERBB2; the disease is breast adenocarcinoma.