Gene Expression Ratio Identifies Risk Of Recurrence In Breast Cancer Patients Receiving Tamoxifen

Researchers from the Massachusetts General Hospital (MGH) Cancer Center and Arcturus Bioscience, Inc., describe their findings in a report to be published in the June issue of Cancer Cell. The paper is being released online today because related material is being presented at the June 5-8 American Society for Clinical Oncology meeting. The study was supported by grants from the Avon Foundation, the U.S. Department of Defense, and the National Cancer Institute.

Tamoxifen, which blocks the interaction between the hormone estrogen and its receptor protein, is used to treat breast cancers that express the estrogen receptor. However, only two thirds of these patients have a prolonged response to the drug. "Until now, there has been no way to predict which estrogen-receptor-positive patients will not respond to tamoxifen treatment," says Dennis Sgroi, MD, director of Breast Pathology at MGH who led the hospital's research team. "Identifying those for whom tamoxifen is likely to fail could allow physicians to choose other drugs, for instance the aromatase inhibitors that more completely block estrogen's action." Sgroi is an associate professor of Pathology at Harvard Medical School.

The hormone estrogen can stimulate both the normal growth of breast tissue and the uncontrolled growth of breast cancer. Cells from most breast tumors contain estrogen receptor molecules, indicating that the tumor's growth is likely to be sensitive to the hormone's action. Estrogen-blocking drugs have been used in recent years to prevent hormone-sensitive breast tumors from recurring after surgery and to treat metastasis. More than 500,000 U.S. women currently take tamoxifen, making it the most frequently used drug of this class.

The MGH and Arcturus research teams have collaborated for several years on studies of the molecular characteristics of breast tumors. Last year they published a study showing that advanced analysis technologies that identify which genes are expressed, or "turned on," in tumors can characterize the tumor's aggressiveness. As a follow-up to that work, the research teams led by Sgroi and Mark Erlander, PhD, Arcturus chief scientific officer, began to investigate whether such molecular signatures could help identify which drugs would be the best options for particular patients.

The researchers gathered tumor samples from patients who had received tamoxifen treatment for early-stage, estrogen-receptor-positive breast cancer. They identified 60 frozen samples suitable for gene expression analysis for which clinical follow-up information was available. Of those 60 patients, 32 had remained disease-free for an average of eight years, while 28 had recurrence of their tumor or metastasis.

Expression profile analysis demonstrated that the ratio between the expression levels of two genes - HOXB13 and IL17BR - was the strongest predictor of whether a tumor would recur. The higher the expression level of HOXB13 and the lower the expression of IL17BR, the greater the chance of tumor recurrence. Data from an additional 20 samples of tamoxifen-treated tumors supported the predictive power of the two-gene expression ratio.

"Many clinical laboratories currently have the capability to utilize Arcturus technology to measure the relative expression of these two genes," says Erlander. "Several centralized laboratories are developing a test that will be available this summer."

Because HOXB13 is known to be overexpressed in some breast tumors, the researchers investigated whether the gene might also play a role in tumor development. Using cells from normal breast tissues, they induced the expression of the HOXB13 gene. Cells in which the gene was activated showed obvious structural changes and appeared to have an increased ability to move and invade other tissues, characteristics of tumor cells. While that result must be confirmed by future studies, it suggests that the pathway controlled by HOXB13 could be a new therapeutic target.

The report's co-authors are first author Xiao-Jun Ma, PhD, Ranelle Salunga, J. Todd Tuggle, Yen Tran, Diem Tran, Ana Sollberger, Paul Amon, Wilson Wang, Wei Wang, Kimberly Stecker, Eden Estepa-Sabal and Thomas Baer, PhD, of Arcturus; Zuncai Wang, PhD, Paula Ryan, MD, PhD, Anne Barmettler, Andrew Fuller, Beth Muir, Gayatry Mohapatra, PhD, Barbara Smith, MD, PhD, Jerry Younger, MD, Ulysses Balis, MD, Atul Bhan, MD, Karleen Habin, RN, and Daniel Haber, MD, PhD, of the MGH; and Steven Isakoff, MD, PhD, and Joan Brugge, PhD, of Harvard Medical School.

Massachusetts General Hospital, established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research program in the United States, with an annual research budget of more than $400 million and major research centers in AIDS, cardiovascular research, cancer, cutaneous biology, medical imaging, neurodegenerative disorders, transplantation biology and photomedicine. In 1994, MGH and Brigham and Women's Hospital joined to form Partners HealthCare System, an integrated health care delivery system comprising the two academic medical centers, specialty and community hospitals, a network of physician groups, and nonacute and home health services.

Arcturus Bioscience, Inc., the leading company in laser microdissection instruments and reagents for the analysis of microscopic tissue samples. These tools enable researchers to perform rapid cell-based analysis of disease progression utilizing the smallest and purest samples possible to date. The company has developed this unique technology platform for genetic analysis of biopsy samples and has applied its platform to discover cell-specific gene signatures associated with human diseases such as cancer. Arcturus is a private company headquartered in Mountain View, California.