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Background: Targeted therapies in HER2-positive metastatic breast cancer significantly improve outcomes but efficacy is limited by therapeutic resistance. HER2 is an acutely sensitive Heat Shock Protein 90 (HSP90) client and HSP90 inhibition can overcome trastuzumab resistance. Preclinical data suggest that HSP90 inhibition is synergistic with taxanes with the potential for significant clinical activity. We therefore tested ganetespib, a HSP90 inhibitor, in combination with paclitaxel and trastuzumab in patients with trastuzumab-refractory HER2-positive metastatic breast cancer.Methods: In this phase I dose-escalation study, patients with trastuzumab-resistant HER2-positive metastatic breast cancer received weekly trastuzumab (2 mg/kg) and paclitaxel (80 mg/m2) on days 1, 8, 15, and 22 of a 28-day cycle with escalating doses of ganetespib (100 mg/m2, 150 mg/m2, and a third cohort of 125 mg/m2 if needed) on days 1, 8, and 15. Therapy was continued until disease progression or toxicity. The primary objective was to establish the safety and maximum tolerated dose and/or recommended phase II dose (RP2D) of this therapy. The secondary objectives included evaluation of the effects of ganetespib on the pharmacokinetics of paclitaxel, and to make a preliminary assessment of the efficacy of the combination therapy.Results: Dose escalation was completed for the two main cohorts without any observed dose-limiting toxicities. Nine patients received treatment. The median prior lines of anti-HER2 therapy numbered three (range 2-4), including prior pertuzumab in 9/9 patients and ado-trastuzumab emtansine (T-DM1) in 8/9 patients. The most common grade 1/2 adverse events (AEs) were diarrhea, fatigue, anemia, and rash. There were no grade 4 AEs related to ganetespib. The overall response rate was 22% (2/9 patients had partial response) and stable disease was seen in 56% (5/9 patients). The clinical benefit rate was 44% (4/9 patients). The median progression-free survival was 20 weeks (range 8-55).Conclusion: The RP2D of ganetespib is 150 mg/m2 in combination with weekly paclitaxel plus trastuzumab. The combination was safe and well tolerated. Despite prior taxanes, pertuzumab, and T-DM1, clinical activity of this triplet regimen in this heavily pretreated cohort is promising and warrants further study in HER2-positive metastatic breast cancer.Trial Registration: ClinicalTrials.gov NCT02060253 . Registered 30 January 2014. [ABSTRACT FROM AUTHOR]

Patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer are at an increased risk of developing brain metastases. The incidence and prevalence of central nervous system (CNS) disease are increasing due to improved survival, which can be attributed to better systemic therapies for extracranial disease. The current standard of care for brain metastases includes a combination of surgery and/or radiation. Systemic therapies are typically reserved for patients with intracranial progression following radiation, due to their limited ability to cross the blood-brain barrier. None of the available anti-HER2 agents (trastuzumab, lapatinib, pertuzumab, and ado-trastuzumab emtansine (T-DM1)) are currently approved for the treatment of brain metastases. Research is underway evaluating novel anti-HER2 agents, which have demonstrated CNS activity. This article discusses the current data on using anti-HER2 therapies to treat CNS disease as well as the newer anti-HER2 agents, which may overcome the current challenges faced in treating brain metastases in the HER2-positive patient population. [ABSTRACT FROM AUTHOR]