Trastuzumab plus GM-CSF for patients with trastuzumab-resistant, HER2-overexpressing metastatic breast cancer: Pilot study

803 Background: Preclinical data suggest that the anti-tumor activity of trastuzumab (Herceptin) is partly due to antibody-dependent cellular cytotoxicity (ADCC) by immune effector cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF, Leukine) enhances ADCC by stimulating a variety of effector cells, including natural killer cells. In this pilot study, we tested the clinical antitumor effect of Herceptin plus GM-CSF in women with Herceptin-resistant metastatic breast cancer. Methods: Eligible patients (pts) had measurable, HER2-overexpressing, metastatic breast cancer; progressive disease (PD) after Herceptin ± chemotherapy; and good performance status (ECOG 0–1). Herceptin was given at 4 mg/kg IV followed by 2 mg/kg every wk for 4 wk (1 cycle). GM-CSF was given at 250 mcg/m2 SC daily until absolute neutrophil count (ANC) >10,000/mm3, then every other day while ANC was below 10,000/mm3. Treatment was continued until PD or intolerable toxicity. The primary endpoint was tumor response (including ...