PURPOSE

Pertuzumab is a humanized monoclonal antibody inhibiting human epidermal growth factor receptor 2 (HER2) dimerization. The aim of this phase II trial was to assess the antitumor activity and safety profile of pertuzumab monotherapy in patients with HER2-negative metastatic breast cancer. The utility of biomarkers detected in paraffin-embedded tissue as predictors of response was also explored.

PATIENTS AND METHODS

This was an international, multicenter, open-label, randomized phase II study. Patients (n = 79) with centrally confirmed HER2-negative metastatic breast cancer were randomly assigned to receive pertuzumab once every 3 weeks with a loading dose of 840 mg followed thereafter by either 420 mg (arm A) or 1,050 mg (arm B). Patients were stratified by country and prior taxane therapy.

RESULTS

Of 79 patients who were randomly assigned, 78 were included in the intent-to-treat population. In arm A (n = 41), two patients had partial responses, and 18 patients (44%) experienced stable disease (SD) lasting > or = 12 weeks. In arm B (n = 37), SD was observed in 14 patients (38%). Overall, six of 78 patients responded or had SD > or = 6 months. Pertuzumab was generally well tolerated, and most adverse events were mild to moderate. Decline in left ventricular ejection fraction of > or = 10% and/or to less than 50% was observed in eight patients, with one case of congestive heart failure in arm A. Pharmacokinetic data supported a fixed dose of pertuzumab once every 3 weeks.

CONCLUSION

The limited efficacy observed in this study, generally SD of relatively short duration, suggested little benefit of further investigation of single-agent pertuzumab in unselected patients with HER2-negative disease.