A combination of the breakthrough drug Keytruda and Herceptin is well tolerated and has clinical benefits for patients with Herceptin-resistant HER2-positive breast cancer.

The new treatment regimen was tested in a clinical trial on patients with advanced HER2-positive breast cancer that had continued to grow on Herceptin (trastuzumab) therapies.

The results were presented at the San Antonio Breast Cancer Symposium and researchers say they suggest that immunotherapy approaches could work in patients with advanced HER2-positive breast cancer that is resistant to Herceptin.

Lead researcher, Dr Sherene Loi says approximately 20 percent of invasive breast cancers are HER2-positive, and some of these patients will develop resistance to trastuzumab.

“We believe that immune evasion is a part of the biological resistance to trastuzumab in patients with this disease. Our prior studies have shown that anti-tumour immunity is important for improved outcomes in patients with advanced HER2-positive breast cancer.”

Dr Loi and colleagues have previously demonstrated that patients with trastuzumab-resistant advanced HER2-positive breast cancer had evidence of poor immune responses.

The new study looked at combining the delivery of Keytruda (pembrolizumab) and Herceptin in women with tumours containing the protein PD1. Keytruda targets this specific protein.

They discovered that those who had the PD1 protein and who also received the combined therapy had a disease control rate of 25 per cent, meaning the cancer had stopped growing.  Furthermore 5 per cent of these patients continued to have no disease progression.

The two drugs were well tolerated, with fatigue being the most commonly reported adverse event.

“This proof-of-principle study suggests that immune evasion is a mechanism of resistance to trastuzumab and contributes to disease progression in advanced HER2-positive breast cancer.

“Our results suggest that PD1 inhibition is likely to become part of the treatment armamentarium of HER2-positive disease in the future,” Dr Loi says.

12 March 2018

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