PD09-08: Combined Inhibition of mTORC1 with Temsirolimus and HER2 with Neratinib: A Phase I/II Study in Patients with Metastatic HER2−Amplified or Triple-Negative Breast Cancer.

Background: Hyperactivation of the PI3K-AKT-mTOR pathway is a postulated mechanism of resistance to anti-HER2 therapies and has also been described in triple-negative breast tumors. In HER2−amplified (HER2+) laboratory models, inhibition of this pathway induces activation of upstream receptor tyrosine kinases such as HER3. In triple-negative breast cancer (TN), HER1 overexpression has been identified and models show sensitivity to combined HER1 and mTOR inhibition. We hypothesize that dual inhibition of the PI3K pathway, HER1/2, and induced HER3 may be highly effective in patients with HER2+ or TN breast cancer (BC). This phase I/II trial is designed to determine the tolerability and possible efficacy of the mTOR inhibitor temsirolimus (T) plus the HER1/2 inhibitor neratinib (N) in patients with trastuzumab-refractory, HER2+ or TN BC. We will also explore mutational activation of the PI3K pathway in trastuzumab-refractory tumors as it relates to response to the T-N combination. Methods: The phase I dose-escalation study evaluated T (flat dose IV weekly) plus N (240 mg oral daily) in patients with metastatic HER2+ or TN BC. Cycle length was 4 weeks. Phase I end points included definition of maximum tolerated dose (MTD) and response rate (RR) per RECIST. The phase II study has a Simon two-stage design and evaluates the HER2+ and TN patients separately. Phase II endpoints include progression free survival and duration of response. Response was evaluated radiographically every 8 weeks, toxicity assessed every 2 weeks. All patients underwent biopsy of metastatic disease for biomarker assessment. Activating mutations in PIK3CA were assayed using the Sequenom MassARRAY system. Expression of PTEN was assessed by immunohistochemistry utilizing a published scoring system. Results: The phase I study enrolled 8 HER2+ patients who received a median of 5 (1-13) cycles of therapy. All patients had received trastuzumab and a median of 5.5 (2-12) prior lines of therapy. Frequent treatment-related grade 2 events were: hyperglycemia (4/8), elevated CPK (3/8), diarrhea (2/8), and rash (2/8). Grade 3 diarrhea was the dose-limiting toxicity. Other grade 3 toxicity was hyperglycemia (1/8); hematologic toxicities were not observed. The MTD of temsirolimus with neratinib is 8 mg IV weekly. Six patients treated at MTD were evaluable for response; 4 patients had PR, 1 had SD for a RR of 67%. PI3K pathway activation, through PIK3CA mutational activation or PTEN loss, was identified in 4/6 tumors analyzed and did not preclude response to temsirolimus and neratinib. Updated results reflecting the phase II patients will be reported. Conclusions: Temsirolimus plus neratinib is active in trastuzumab-refractory HER2+ patients. The phase II study is ongoing and additional efficacy and safety data in both HER2−amplified and triple-negative breast cancer patients will be presented. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD09-08.