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Original Investigation
November 23, 2016

Targeting the PI3K/AKT/mTOR Pathway for the Treatment of Mesenchymal Triple-Negative Breast CancerEvidence From a Phase 1 Trial of mTOR Inhibition in Combination With Liposomal Doxorubicin and Bevacizumab

Author Affiliations
  • 1Division of Cancer Medicine, The University of Texas MD Anderson Cancer Center, Houston
  • 2Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston
  • 3Breast Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston
  • 4Investigational Cancer Therapeutics (Phase I Trials Program), The University of Texas MD Anderson Cancer Center, Houston
  • 5Sheikh Khalifa Bin Zayed Al Nahyan Institute for Personalized Cancer Therapy, The University of Texas MD Anderson Cancer Center, Houston
  • 6Breast Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston
  • 7Biostatistics, The University of Texas MD Anderson Cancer Center, Houston
  • 8Pediatrics, The University of Texas MD Anderson Cancer Center, Houston
  • 9Health Services Research, The University of Texas MD Anderson Cancer Center, Houston
  • 10Division of Hematology and Oncology, University of California San Diego Moores Cancer Center, La Jolla
JAMA Oncol. Published online November 23, 2016. doi:10.1001/jamaoncol.2016.5281
Key Points

Question  Using metaplastic breast cancer as a surrogate, is phosphoinositide 3-kinase (PI3K) pathway–directed therapy effective in the treatment of mesenchymal triple-negative breast cancer (TNBC)?

Findings  In this cohort of patients with metaplastic TNBC, the combination of liposomal doxorubicin, bevacizumab, and the mammalian target of rapamycin inhibitors temsirolimus or everolimus had a higher objective response rate than has historically been seen in this chemorefractory subset of tumors. There was a high incidence of PI3K pathway aberrations, and patients whose tumors had pathway aberrations had a significantly higher objective response rate compared with patients with tumors lacking pathway aberrations.

Meaning  Further investigation of PI3K pathway–directed therapy is warranted in the treatment of metaplastic TNBC, as well as mesenchymal TNBC as a whole, once diagnostic assays are available.

Abstract

Importance  Triple-negative breast cancer (TNBC) classified by transcriptional profiling as the mesenchymal subtype frequently harbors aberrations in the phosphoinositide 3-kinase (PI3K) pathway, raising the possibility of targeting this pathway to enhance chemotherapy response. Up to 30% of mesenchymal TNBC can be classified histologically as metaplastic breast cancer, a chemorefractory group of tumors with a mixture of epithelial and mesenchymal components identifiable by light microscopy. While assays to identify mesenchymal TNBC are under development, metaplastic breast cancer serves as a clinically identifiable surrogate to evaluate potential regimens for mesenchymal TNBC.

Objective  To assess safety and efficacy of mammalian target of rapamycin (mTOR) inhibition in combination with liposomal doxorubicin and bevacizumab in patients with advanced metaplastic TNBC.

Design, Setting, and Participants  Phase 1 study with dose escalation and dose expansion at the University of Texas MD Anderson Cancer Center of patients with advanced metaplastic TNBC. Patients were enrolled from April 16, 2009, to November 4, 2014, and followed for outcomes with a cutoff date of November 1, 2015, for data analysis.

Interventions  Liposomal doxorubicin, bevacizumab, and the mTOR inhibitors temsirolimus or everolimus using 21-day cycles.

Main Outcomes and Measures  Safety and response. When available, archived tissue was evaluated for aberrations in the PI3K pathway.

Results  Fifty-two women with metaplastic TNBC (median age, 58 years; range, 37-79 years) were treated with liposomal doxorubicin, bevacizumab, and temsirolimus (DAT) (N = 39) or liposomal doxorubicin, bevacizumab, and everolimus (DAE) (N = 13). The objective response rate was 21% (complete response = 4 [8%]; partial response = 7 [13%]) and 10 (19%) patients had stable disease for at least 6 months, for a clinical benefit rate of 40%. Tissue was available for testing in 43 patients, and 32 (74%) had a PI3K pathway aberration. Presence of PI3K pathway aberration was associated with a significant improvement in objective response rate (31% vs 0%; P = .04) but not clinical benefit rate (44% vs 45%; P > .99).

Conclusions and Relevance  Using metaplastic TNBC as a surrogate for mesenchymal TNBC, DAT and DAE had notable activity in mesenchymal TNBC. Objective response was limited to patients with PI3K pathway aberration. A randomized trial should be performed to test DAT and DAE for metaplastic TNBC, as well as nonmetaplastic, mesenchymal TNBC, especially when PI3K pathway aberrations are identified.

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