Abstract
Phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway activation in patients with HER2-positive (HER2(+)) breast cancer has been implicated in de novo and acquired trastuzumab resistance. The purpose of this study was to determine the clinical activity of the PI3K inhibitor buparlisib (BKM120) in patients with HER2(+) advanced/metastatic breast cancer resistant to trastuzumab-based therapy. In the dose-escalation portion of this phase I/II study, patients with trastuzumab-resistant locally advanced or metastatic HER2(+) breast cancer were treated with daily oral doses of buparlisib and weekly intravenous trastuzumab (2 mg/kg). Dose escalation was guided by a Bayesian logistic regression model with overdose control. Of 18 enrolled patients, 17 received buparlisib. One dose-limiting toxicity of grade 3 general weakness was reported at the 100-mg/day dose level (the single-agent maximum tolerated dose) and this dose level was declared the recommended phase II dose (RP2D) of buparlisib in combination with trastuzumab. Common (>25%) adverse events included rash (39%), hyperglycemia (33%), and diarrhea (28%). The pharmacokinetic profile of buparlisib was not affected by its combination with trastuzumab. At the RP2D, there were two (17%) partial responses, 7 (58%) patients had stable disease (≥6 weeks), and the disease control rate was 75%. Pharmacodynamic studies showed inhibition of the PI3K/AKT/mTOR and RAS/MEK/ERK pathways. In this patient population, the combination of buparlisib and trastuzumab was well tolerated, and preliminary signs of clinical activity were observed. The phase II portion of this study will further explore the safety and efficacy of this combination at the RP2D. Clin Cancer Res; 20(7); 1935-45. ©2014 AACR.
Highlights
HER2 is overexpressed in 15% to 30% of breast cancers, and is associated with aggressive disease and poor prognosis [1,2,3]
The pharmacokinetic profile of buparlisib was not affected by its combination with trastuzumab
Clinical responses to buparlisib and trastuzumab were reported in patients with phosphoinositide 3-kinase (PI3K) pathway–activated tumors, and evidence of inhibition of both the PI3K/ AKT/mTOR and RAS/MEK/ERK signaling pathways in patients treated with this combination was observed
Summary
HER2 is overexpressed in 15% to 30% of breast cancers, and is associated with aggressive disease and poor prognosis [1,2,3]. Use of the HER2 antibody trastuzumab has led to important clinical benefits for patients with HER2positive (HER2þ) breast cancer, 50% to 74% of patients with metastatic disease do not respond to treatment [4, 5], and approximately 75% progress within a year [4]. These treatment options have been shown to offer some additional benefit, with objective response rates of 22%, 24%, and 44%, respectively, and median progression-free survival times of 8.4, 5.5, and, 9.6 months, respectively [6,7,8]. Activation of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway is observed in approximately 75% of HER2þ breast cancers Inhibition of this pathway has been shown to restore sensitivity to trastuzumab in resistant breast cancer models. Clinical responses to buparlisib and trastuzumab were reported in patients with PI3K pathway–activated tumors, and evidence of inhibition of both the PI3K/ AKT/mTOR and RAS/MEK/ERK signaling pathways in patients treated with this combination was observed
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