Novel Combination Therapy Shows Promise in Treating Metastatic Estrogen Receptor Positive Breast Cancer

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Research findings from a phase Ib/II trial have revealed promising results for a novel combination therapy in treating metastatic estrogen receptor positive breast cancer. The study, conducted at Vanderbilt University Medical Center, evaluated the clinical activity and safety of atezolizumab in combination with either cobimetinib or idasanutlin in patients with metastatic estrogen receptor positive breast cancer. Although the trial was limited by small sample sizes, the researchers observed notable clinical activity, including durable responses to treatment and conservation of tumor-specific HLA-ABC expression in patients with clinical benefit.

Key Takeaways:

  • The study examined the clinical activity and safety of atezolizumab in combination with either cobimetinib or idasanutlin in patients with metastatic estrogen receptor positive breast cancer.
  • The trial enrolled 12 patients, but was closed early due to slow accrual.
  • 2/7 patients in arm IDA had durable responses to treatment, while 1/5 patients in arm COBI had stable disease.
  • Conservation of tumor-specific HLA-ABC expression was observed in nearly all patients with clinical benefit.
  • Grade 3-4 toxicities, particularly cytopenias, were reported in arm IDA.
  • The study observed notable clinical activity, including one exceptional responder, that warrants further investigation.
  • Jessica Mezzanotte-Sharpe and colleagues' research suggests potential for this novel combination therapy in treating metastatic estrogen receptor positive breast cancer.
  • The study received funding from the Vanderbilt Oncology Training Program T32 and the Stand Up To Cancer- Genentech Catalyst Research Grant.

Statistics:

  • 12 patients were enrolled in the phase Ib/II trial.
  • 2/7 patients in arm IDA had durable responses to treatment.
  • 1/5 patients in arm COBI had stable disease.
  • Nearly all patients with clinical benefit showed conservation of tumor-specific HLA-ABC expression.
  • Grade 3-4 toxicities were reported in 5/12 patients in arm IDA.

Sources:

  • A phase Ib/II trial of atezolizumab with cobimetinib or idasanutlin in metastatic estrogen receptor positive breast cancer. npj Breast Cancer, 2025,11(1):1-9. (npj Breast Cancer - https://www.nature.com/npjbcancer/). Published by Nature Portfolio.
  • NewsRx. Research from Vanderbilt University Medical Center Provides New Data on Breast Cancer (A phase Ib/II trial of atezolizumab with cobimetinib or idasanutlin in metastatic estrogen receptor positive breast cancer). Immunotherapy Weekly. July 9, 2025; p 516.