Multi-drug inhibition of the HER pathway in metastatic colorectal cancer: Results of a phase I study of pertuzumab plus cetuximab in cetuximab-refractory patients

Purpose: Resistance to cetuximab, a monoclonal antibody against the epithelial growth factor receptor (EGFR), in colorectal cancer (CRC) may result from compensatory signaling through ErbB receptors, ErbB2/neu/HER2 (HER2) and ErbB3/HER3 (HER3). Pertuzumab is a monoclonal antibody that blocks HER2 hetero-dimerization; thus the combination of pertuzumab and cetuximab could possibly overcome cetuximab resistance. Patients and methods: This single-arm, open-label,multicenter phase I/II study was designed to assess the safety and efficacy of pertuzumab and cetuximab in patients with cetuximab-resistant KRAS wild type metastatic CRC. Thirteen patients were enrolled and received cetuximab in combination with pertuzumab at several dose levels in a 3+ 3 design. Patients were assessed for dose-limiting toxicity (DLT) during the first cycle. A phase II portion was planned, but not initiated due to toxicity. Results: Six of the thirteen patients (46 %) experienced DLTs, therefore the study was terminated early. Grade 3 or higher DLTs included dermatitis with desquamation and/or acneiform rash (n=6), mucositis or stomatitis (n=5), and diarrhea (n=2). There was one Grade 5 event (myocardial infarction) attributed to underlying disease. Among the 13 patients, seven (54 %) were evaluable for response. The objective response rate was 14 %: one patient had a partial response lasting 6 months. Two patients had stable disease (29 %), and four had progressive disease (57 %). Median progression free survival was 2.1 months (95 % CI, 1.5-4.9) and median overall survival was 3.7 months (95 % CI, 1.6-7.9). Conclusion: Combination pertuzumab and cetuximab in refractory CRC was associated with potential antitumor activity; however, the combination was not tolerable due to overlapping toxicities.