This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast cancer is the most commonly diagnosed cancer in women, and most women are diagnosed before the disease spreads throughout the body. The number of women dying from the disease has been decreasing, in part because more effective treatments for the disease are now available. For women with early stage cancer that has hormone receptors on the surface of the tumor, tamoxifen has been the standard hormone treatment for more than 20 years. Aromatase inhibitors, which block the production of the estrogen hormone in the body, have recently been found to be more effective than tamoxifen in early breast cancer. This study will evaluate two different aromatase inhibitors, exemestane (Aromasin) and letrozole (Femara). These medications have similar effects on estrogen production but have different chemical structures and work in slightly different ways and therefore may differ in both their effect against the cancer and their side effects. This study will evaluate aromatase inhibitors in post-menopausal women with early stage breast cancer that expresses hormone receptors who have either never taken tamoxifen or who have previously taken tamoxifen for a total of 1-5 years. The patients who enroll would be starting aromatase inhibitors for treatment of their breast cancer even if they were not participating in the trial. Our trial will include approximately 500 women at three centers in the United States, including the University of Michigan. Study participants will be randomly assigned to take either exemestane or letrozole daily for two years. The primary goal of the study is not to evaluate effectiveness of the medications, but rather to look at the levels of the medication in the body, as well as the effects of the medication on hormone levels, breast density, bone health, and cholesterol levels. We will also evaluate side effects, including hot flashes and bone and joint discomfort. Another aspect of the study will involve evaluation of patient DNA, the substance that carries an individual s genetic information, to determine if differences in DNA affect response to treatment or side effects from the medications. We will analyze genes (segments of DNA) those involved in bone health, hot flashes, breakdown of the aromatase inhibitor medication, and regulation and processing of hormones including estrogen. Our long-term goal is to determine if a particular aromatase inhibitor may be more effective or have fewer side effects in a specific patient depending on her genetic make-up.
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