Solving treatment resistance in most common breast cancer

Published in the Annals of Oncology, the research identifies the presence of ER gene (ESR1) fusion proteins in treatment-resistant breast cancer. This is the first time that recurrent ESR1 fusion proteins have been identified in human breast cancer, and understanding how they function could lead to improved treatments for the disease.

"We first identified this change in a patient who had ER-positive breast cancer, received anti-estrogen therapy, had her breast cancer recur and eventually passed away from the disease," said senior author Adrian Lee, Ph.D., director of the Women's Cancer Research Center at MWRI and UPMC Hillman Cancer Center, and professor of Pharmacology & Chemical Biology at the University of Pittsburgh. "A member of our lab noticed the mutation while performing posthumous genetic analysis from tissue in our organ donation program, and over time we were able to identify many more cases of this mutation in patients with recurrent disease." This work was performed in collaboration with Foundation Medicine Inc., a genomic testing company that examined ESR1 fusions in close to 10,000 breast cancers sequenced with the FoundationOne CDx test.

According to Lee, ESR1 fusion proteins "outsmart" traditional treatment by splitting in half and eliminating the binding site that anti-estrogen therapy targets.

"Physicians will continue administering anti-estrogen therapy, not realizing this genetic mutation has occurred," said Lee. "Now that we understand the change, though, we can detect it with a blood test and help improve treatments for this form of the disease."

According to Lee, genetic analysis will soon be the dominant field of ER-positive breast cancer research, eventually leading to improved treatments and patient outcomes.

"Genomic sequencing is telling us so much about breast cancer. I believe the research we are doing in the laboratory will have a significant clinical impact in the near future, and the work we are doing will play a large part in improving patient care and survival," said Lee.

Lead authors on this research are Ryan J. Hartmaier, Ph.D., of Pitt, MWRI and Foundation Medicine Inc., and Sally E. Trabucco, Ph.D., of Foundation Medicine Inc.

This research was funded by U.S. Department of Defense Congressionally Directed Medical Research Programs fellowship W81XWH-11-1-0582, Fashion Footwear of New York and the Breast Cancer Research Foundation. This project used services and equipment supported by National Institutes of Health (NIH) awards P30CA047904, UL1-RR024153 and UL1-TR000005. Additional support is from Scientific Advisory Council award SAC150021 from Susan G. Komen for the Cure and the Hillman Foundation, as well as NIH training grant 2T32GM008424-21 and fellowship 5F30CA203095.