An exploratory study of sunitinib in combination with docetaxel and trastuzumab as first-line therapy for HER2-positive metastatic breast cancer

Background: This exploratory study assessed the safety, pharmacokinetics, and antitumor activity of sunitinib combined with docetaxel and trastuzumab. Methods: Patients with unresectable, locally recurrent or metastatic human epidermal growth factor receptor 2 (HER2)+ breast cancer received sunitinib plus docetaxel and trastuzumab. Sunitinib was administered at 37.5 mg/day for 2 weeks on treatment followed by 1 week off (Schedule 2/1). The primary endpoint was safety; secondary endpoints included pharmacokinetics and antitumor activity. Results: Twenty-six patients enrolled; 24 received at least one dose of sunitinib plus docetaxel and trastuzumab, and one patient received one dose of docetaxel and trastuzumab only. These 25 treated patients were evaluable for safety. Twenty-three patients discontinued the study, primarily due to disease progression. The planned dose of sunitinib was maintained in 10 patients and reduced at least once to 25 mg/day in 14 patients. The most common grade 3/4 non-hematologic adverse events were fatigue/asthenia (28%), diarrhea (16%), stomatitis (12%), vomiting (8%) and dyspnea (8%). Neutropenia was reported in all 24 evaluable patients; most events were grade 4. Three grade 1-3 cardiac adverse events occurred. Sunitinib and docetaxel levels were consistent with known single-agent levels, suggesting that there were no clinically relevant drug-drug interactions. Of 22 evaluable patients, 16 (73%) experienced an objective response (all confirmed partial responses). Conclusions: Sunitinib combined with docetaxel and trastuzumab had an acceptable toxicity profile and showed preliminary antitumor activity as first-line treatment for metastatic HER2+ breast cancer.