PRIMARY OBJECTIVE:~I. To comprehensively evaluate differences in tumor microenvironment subpopulations in aromatase inhibitor (AI)-sensitive versus (vs.) AI-resistant hormone receptor (HR)+ breast cancer.~SECONDARY OBJECTIVES:~I. To assess the effects of estrogen deprivation on the systemic immune response.~II. To assess the effects of estrogen deprivation on tumor immune microenvironment.~OUTLINE:~Patients receive letrozole orally (PO) once daily (QD) for 2-8 weeks prior to surgery in the absence of disease progression or unacceptable toxicity. Patients then undergo collection of blood and tissue samples.
This phase II trial examines letrozole in patients with hormone receptor positive, HER2 negative breast cancer that can be removed by surgery (operable). Letrozole is in a class of medications called nonsteroidal aromatase inhibitors. It works by decreasing the amount of estrogen produced by the body. This can slow or stop the growth of some types of breast cancer cells that need estrogen to grow.