The cytotoxicity of ADC11 was measured against cancer cell lines with various levels of Her2 expression and the ADC was found to be extremely potent against Her2 expressing N87 (IC50 = 0.49 nM) and 361 (IC50 = 0.39 nM) cell lines and exhibited approximately 1000 fold selectivity against the non-Her2 expressing 468 cell line. The gene discussed is ERBB2; the disease is cancer.