For women with a very aggressive form of breast cancer, a newly discovered biomarker could indicate how much they might benefit from a recently approved drug.
In a Phase III clinical trial that led the FDA to approve trastuzumab emtansine (T-DM1) on Feb. 22, researchers at Memorial Sloan-Kettering Cancer Center in New York City discovered that the amount of the protein HER2 on patients' tumor might determine how they will respond to the new drug. An alteration in the HER2 gene, which is found in normal cell growth, plays a key role in the growth of metastatic, HER2-positive breast cancer
Researchers measured the amount of HER2 messenger ribonucleic acid (mRNA) in tissue samples of clinical trial participants to see whether tumor levels of HER2 affected reponses to treatment. Patients' tumor tissue that had greater than the average amount of tumor HER2 mRNA were considered to have high levels of HER2. Conversely, those who had tumors with the average amount of tumor HER2 RNA or less had low levels of HER2.
"Even though everyone enrolled in the clinical trial had breast cancer expressing elevated levels of HER2, we know that each person's tumor has different molecular features," Dr. José Baselga, physician-in-chief at Memorial Sloan-Kettering Cancer Center, said in a statement. "Even the degree to which HER2 expression is elevated differs from patient to patient."
When Baselga and his team treated patients with T-DM1, those with tumors expressing higher levels of HER2 benefited from the drug compared to patients whose tumors had lower levels of HER2. Patients with high levels of HER2 lived 34.1 months longer versus 26.5 months. Patients with higher levels of HER2 also had a 47% decreased risk for death when treated with T-DM1 compared to those who received lapatinib and capecitabine.
The findings were presented at the American Association for Cancer Research annual meeting in Washington, D.C., this month.
- here's the press release
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