Adding paclitaxel to trastuzumab enhances antibody-dependent cell-mediated cytotoxicity via increment of natural killer cells in patients with Her-2 overexpressing breast cancer

10548 Background: One of the mechanisms by which trastuzumab (TZ) inhibits the growth of Her-2 overexpressing breast cancer cells is the activation of a host tumor response via antibody-dependent cell-mediated cytotoxicity (ADCC). We questioned whether adding PTX to TZ enhances ADCC and also investigated kinetics of effector cells in ADCC. Methods: In ADCC, 5 cases with metastatic breast cancer receiving TZ (4mg/kg as a loading and 2 mg/kg weekly) with PTX (2qw, 100 mg/m2) were investigated. ADCC was analyzed by 51Cr releasing assay using SK-BR-3 cell line and white blood cells taken at the time of pretreatment, after 4 mg/kg of TZ, before/after 2 mg/kg of TZ, and before/after 2 mg/kg of TZ plus PTX. In of effector cell studies, we investigated fractions of natural killer (NK) cell, monocyte, and neutrophil taken at pre-administration and 10 minutes post-administration in 16 patients with Her-2 overexpressing breast cancer receiving weekly TZ and PTX (80 mg/m2). We defined NK cells as being both CD16+ (Fc...