Pertuzumab monotherapy after trastuzumab-based treatment and subsequent reintroduction of trastuzumab: activity and tolerability in patients with advanced human epidermal growth factor receptor 2-positive breast cancer.

Purpose The combination of pertuzumab and trastuzumab resulted in a clinical benefit rate (CBR) of 50% in patients with human epidermal growth factor receptor 2 (HER2) –positive breast cancer whose disease progressed during prior trastuzumab-based therapy. To define whether this previously observed encouraging activity was a result of the combination of pertuzumab and trastuzumab or of pertuzumab alone, we recruited a third cohort of patients who received pertuzumab without trastuzumab. We then investigated the impact of reintroducing trastuzumab to patients whose disease progressed on pertuzumab monotherapy. Patients and Methods Twenty-nine patients with HER2-positive breast cancer whose d…