Oncogenic PIK3CA-driven mammary tumors frequently recur via PI3K pathway–dependent and PI3K pathway–independent mechanisms

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PIK3CA gain-of-function mutations are a common oncogenic event in human malignancy1,2,3,4, making phosphatidylinositol 3-kinase (PI3K) a target for cancer therapy. Despite the promise of targeted therapy, resistance often develops, leading to treatment failure. To elucidate mechanisms of resistance to PI3K-targeted therapy, we constructed a mouse model of breast cancer conditionally expressing human PIK3CAH1047R. Notably, most PIK3CAH1047R-driven mammary tumors recurred after PIK3CAH1047R inactivation. Genomic analyses of recurrent tumors revealed multiple lesions, including focal amplification of Met or Myc (also known as c-Met and c-Myc, respectively). Whereas Met amplification led to tumor survival dependent on activation of endogenous PI3K, tumors with Myc amplification became independent of the PI3K pathway. Functional analyses showed that Myc contributed to oncogene independence and resistance to PI3K inhibition. Notably, PIK3CA mutations and c-MYC elevation co-occur in a substantial fraction of human breast tumors. Together, these data suggest that c-MYC elevation represents a potential mechanism by which tumors develop resistance to current PI3K-targeted therapies.

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Download references


We thank T. Roberts, L. Cantley and W. Sellers for scientific discussions and suggestions. We thank L. Clayton and D. Silver for critical review of this manuscript. We thank R. Bronson for pathological analyses of tumor samples. We thank C. Li and E. Allgood for technical assistance. We thank L. Chodosh (University of Pennsylvania School of Medicine) for providing MMTV-rtTA mice. This work was supported by US National Institutes of Health grants CA134502 (J.J.Z.), CA148164-01 (J.J.Z. and N.S.G.) and K08CA122833 (R.B.), Stand Up To Cancer (J.J.Z. and G.B.M.), Dana Farber Harvard Cancer Center breast cancer SPORE grant P50 CA089393-08S1 (J.J.Z.), the US Department of Defense (BC051565 to J.J.Z.), the V Foundation (J.J.Z. and R.B.) and the Claudia Barr Program (J.J.Z.). In compliance with Harvard Medical School guidelines, we disclose that J.J.Z. and R.B. are consultants for Novartis Pharmaceuticals.

Author information

Author notes

    • Pixu Liu
    •  & Hailing Cheng

    These authors contributed equally to this work.


  1. Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.

    • Pixu Liu
    • , Hailing Cheng
    • , Stephanie Santiago
    • , Maria Raeder
    • , Adam Isabella
    • , Janet Yang
    • , Derek J Semaan
    • , Nathanael S Gray
    • , Rameen Beroukhim
    •  & Jean J Zhao
  2. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.

    • Pixu Liu
    • , Hailing Cheng
    • , Stephanie Santiago
    • , Nathanael S Gray
    •  & Jean J Zhao
  3. Department of Surgery, Brigham and Women's Hospital, Boston, Massachusetts, USA.

    • Hailing Cheng
    •  & Jean J Zhao
  4. Department of Obstetrics and Gynecology, Haukeland University Hospital and Department of Clinical Medicine, University of Bergen, Bergen, Norway.

    • Maria Raeder
  5. Department of Systems Biology, University of Texas M.D. Anderson Cancer Center, Houston, Texas, USA.

    • Fan Zhang
    •  & Gordon B Mills
  6. Microarray Core, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.

    • Changzhong Chen
    •  & Edward A Fox
  7. Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.

    • Edward A Fox
    •  & Rameen Beroukhim
  8. Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA.

    • Edward A Fox
    •  & Rameen Beroukhim
  9. Novartis Institutes for Biomedical Research, Cambridge, Massachusetts, USA.

    • John Monahan
    •  & Robert Schlegel
  10. Broad Institute, Cambridge, Massachusetts, USA.

    • Rameen Beroukhim


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P.L., H.C. and J.J.Z. designed the experiments, interpreted the data and wrote the paper. P.L. and H.C. carried out most of the experiments. S.S., A.I. and D.J.S. assisted with biochemical analyses and mouse work. J.Y., C.C., E.A.F., J.M. and R.S. carried out genome-wide DNA copy number profiling. N.S.G. provided GDC-0941 inhibitor. M.R. and R.B. analyzed co-occurrence of PIK3CA mutation with c-MYC amplification and overexpression in human breast tumors. F.Z. and G.B.M. provided the reverse-phase protein array data on the co-occurrence of PIK3CA mutation with increased c-MYC expression in human breast tumors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jean J Zhao.

Supplementary information

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  1. 1.

    Supplementary Text and Figures

    Supplementary Figures 1–16, Supplementary Tables 1–3 and Supplementary Methods