Combination sirolimus and trastuzumab is well-tolerated in patients with metastatic human epidermal growth factor receptor  (HER2)-positive breast cancer after disease progression with prior trastuzumab therapy, according to a study published in Breast Cancer Research and Treatment.

In a phase II trial, researchers led by Carlos Acevedo-Gadea, MD, of the Yale University School of Medicine administered sirolimus 6 mg oral daily along with a standard dose of trastuzumab weekly or every three weeks.

In total, eleven patients were evaluated for safety, and nine were evaluated for response assessment.

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They found that five patients who were treated for 101 weeks had achieved stable disease as best response, while one patient who received eight cycles achieved a partial response.

Overall response rate amounted to 11 percent while clinical benefit rate was 44%.

“Sirolimus 6 mg administered daily with trastuzumab appears to be well-tolerated in patients with metastatic HER2-positive breast cancer following disease progression on prior trastuzumab therapy, with evidence of disease activity,” the authors concluded.


  1. Acevedo-Gadea, Carlos. “Sirolimus and trastuzumab combination therapy for HER2-positive metastatic breast cancer after progression on prior trastuzumab therapy.” Breast Cancer Research and Treatment. DOI: 10.1007/s10549-015-3292-8. February 17, 2015.