The researchers showed that ESR1 mutations could be detected using polymerase chain reaction analysis, an ultra-sensitive test that can read the genetic code of small amounts of DNA released by tumors. The test was able to detect DNA errors as sensitively as tumor biopsies with a 97% match between the 2 tests.

Once ESR1 mutations were discovered, mutated cancer cells multiplied and became the dominant type in the body, making the disease more aggressive and advance rapidly. Women whose breast cancers had ESR1 mutations were more likely to have disease progression.

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Aromatase Inhibitor Resistance

ESR1 mutation prevalence depended on whether patients received aromatase inhibitors in the adjuvant or metastatic settings (5.8% vs 36.4%, respectively; P = .0002).

Analysis of an independent cohort revealed that ESR1 mutations were identified in 0% (95% CI, 0 – 10.9) of patients who had progressed following adjuvant therapy with aromatase inhibitors. The findings suggest that hormonal therapy offers little benefit for patients with metastatic breast cancer.

“The message here is that researchers are able to learn about gene mutations in tumors by analyzing minute quantities of tumor DNA in blood samples, rather than requiring tissue samples acquired by an invasive biopsy,” Dr. Erica Mayer, MD, MPH, of Dana-Farber Cancer Institute in Boston, MA, and an American Society of Clinical Oncology expert in breast cancer, told Cancer Therapy Advisor.

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“Integration of the cfDNA test into a future clinical trial might be a way to identify patients who are less likely to derive benefit from aromatase inhibitors and in whom alternative medications in development, for example the oral selective estrogen receptors degraders, could be tested.”


  1. Schiavon, G, Hrebien, S, Garcia-Murillas, I, et al. Analysis of ESR1 mutation in circulating tumor DNA demonstrates evolution during therapy for metastatic breast cancer. Sci Trans Med. 2015;7(313):313ra182.