Final Results of ECOG1100: A phase I/II study of combined blockade of the ErbB receptor network in patients with HER2- overexpressing metastatic breast cancer (MBC)
1033 Background: Activation of EGF receptor has been associated with resistance to trastuzumab in breast cancer cell lines. EGFR tyrosine kinase inhibitors inhibit HER2 phosphorylation and synergize with trastuzumab in HER2+ cell lines that co-express EGFR. Methods: Pts with MBC and HER2 overexpression by immunohistochemistry (3+) and/or HER2 gene-amplification by FISH, 0–2 prior chemotherapy regimens for met disease, LVEF 50%, and no prior trastuzumab were treated with trastuzumab 2 mg/kg/wk and gefitinib 250- 500 mg/day until disease progression, unacceptable toxicity or withdrawal of consent. The phase I portion of the trial used a 3+3 design to determine MTD. In the phase II portion of the trial, patients were stratified based upon prior chemotherapy exposure (Group 1= no prior exposure to chemotherapy, Group 2= prior exposure to 1–2 chemotherapy regimens). Response measured using RECIST criteria. The primary endpoint was to increase proportion progression free from 50 to 65% at 6 months in Group 1 and from 50 to 70% at 3 months in Group 2. Results: Phase I: DLT (Grade 3 diarrhea) occurred in 2/3 patients treated at the 500 mg/day dose level of gefitinib in combination with weekly trastuzumab. 0/3 patients treated at the 250 mg/day dose level experienced DLT. This was considered MTD and was the dose selected for the Phase II portion of the trial. Phase II: 36 eligible pts were enrolled. Most patients were ECOG PS of 0 and had visceral organ involvement. Of the patients enrolled in Group 1, one pt achieved a CR, one PR and 7 had SD (≥ 24 weeks). Median time to progression (TTP) was 2.9 months (95% CI, 2.5–4). In Group 2 no responses were observed with a median TTP of 2.5 months (95% CI, 1.5- 2.7). Most common severe toxicities were rash (grade 3, 14%) and diarrhea (grade 3, 30%). No grade 3 cardiac toxicity was encountered. Conclusions: Trastuzumab in combination with gefitinib at doses of 250 mg/day demonstrated an acceptable toxicity profile; however, during planned interim analysis, the TTP did not meet predetermined statistical endpoints required for study continuation. These results do not support the further use of this combination and have implications for other trials using trastuzumab and EGFR TK inhibitors simultaneously. [Table: see text]