New Test May Spot Breast Cancer Treatment Resistance

Blood test may detect when breast cancer becomes resistant to aromatase inhibitor treatment

(RxWiki News) Drug resistance is often inevitable in breast cancer treatment. But a new test may be able to identify which patients have become resistant.

A team of researchers from the UK has developed a highly sensitive blood test that could be able to detect when breast cancer has become resistant to aromatase inhibitors (AIs), a class of drugs often used to treat women with estrogen receptor positive (ER+) advanced breast cancer.

The test is designed to detect mutations in the estrogen receptor gene ESR1, which reveals resistance to hormone therapies like AIs. According to these researchers, detecting ESR1 mutations could allow doctors to more quickly identify which patients are no longer benefiting from treatment and switch them to another drug.

"Looking for cancer DNA in the blood allows us to analyse the genetic changes in cancer cells without the need for invasive biopsies," said lead study author Nicholas C. Turner, MD, a molecular oncologist at the UK Institute of Cancer Research and the Royal Marsden NHS Foundation Trust, in a press release. "The test could give doctors an early warning of treatment failure and, as clinical trials of drugs that target ESR1 mutations are developed, help select the most appropriate treatment for women with advanced cancer."

Walker Winn, PharmD, told RxWiki News that oncologists use "multiple factors" to determine whether treatment resistance has developed.

"Once breast cancer is determined to be resistant to the drug therapy being used, the decision is often made to move to second-line treatment options or combinations of multiple drug therapies, which may not be as effective the first-line treatments and may also have a more unfavorable side effect profile," Dr. Winn said.

For this study, Dr. Turner and team took blood samples from 171 women with ER+ advanced breast cancer. These women were then compared to three independent groups of patients.

These researchers found that ESR1 mutations could be detected using a highly sensitive test called a multiplexed digital PCR analysis with about as much accuracy as a tumor biopsy. In other words, the test was able to read the genetic code of tiny amounts of DNA released by tumors into the bloodstream with results matching those of biopsies 97 percent of the time.

Once these mutations were detected, cancer cells were also found to multiply and become dominant — a change that drives cancer to progress faster. The women with ESR1 mutations were three times more likely to have cancers that progressed than those without these mutations.

According to Dr. Turner and team, this finding suggests that more advanced breast cancers develop drug resistance more often than less advanced ones — reinforcing the importance of early diagnosis and treatment.

In the future, this test could potentially reduce the need for invasive surgery to diagnose treatment resistance in breast cancer patients, Dr. Turner and team said.

This study was published Nov. 11 in the journal Science Translational Medicine.

The Royal Marsden NHS Foundation Trust, UK Institute of Cancer Research, Breast Cancer Now, Cancer Research UK and Susan G. Komen Foundation, among others, funded this research.

Several study authors disclosed ties to companies that make products used in breast cancer treatment.

Review Date: 
November 12, 2015