(ChemotherapyAdvisor) – The combination of pertuzumab and trastuzumab was found to be more active than pertuzumab monotherapy in patients with HER2-positive breast cancer that progressed during treatment with trastuzumab, a study in the Journal of Clinical Oncology published online March 5 has found.

Previously, a clinical benefit rate of 50% was observed in women with HER2-positive breast cancer whose disease progressed during prior trastuzumab-based therapy and were subsequently treated with pertuzumab + trastuzumab. To determine whether this was the result of the pertuzumab + trastuzumab combination or pertuzumab alone, this study investigated the impact of reintroducing trastuzumab to patients whose disease had progressed on pertuzumab monotherapy.

Of the 29 patients who received pertuzumab 840mg loading dose followed by 420mg every three weeks, all experienced disease progression; objective response rate was 3.4% and the clinical benefit rate, 10.3%. Among 17 patients with disease progression who continued to receive pertuzumab at the same dose with the addition of trastuzumab 4mg/kg loading dose and 2mg/kg weekly or 8mg/kg loading dose and 6mg/kg every three weeks, the overall response rate was 17.6% and the clinical benefit rate, 41.2%.

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Progression-free survival was 17.4 weeks with the combination therapy and 7.1 weeks with pertuzumab monotherapy. Minimal cardiac dysfunction was observed.

“Our findings suggest that combining anti-HER receptor monoclonal antibodies may result in an improved receptor blockade and a better clinical outcome,” the authors concluded.