Approximately 70% of breast cancers express estrogen receptor alpha (ER), which is activated by estrogens and typically drives cancer cell growth. Adjuvant therapy with anti-estrogens such as tamoxifen and aromatase inhibitors (AIs) is commonly used to inhibit ER to prevent cancer (re)growth after early-stage breast tumors are surgically removed. However, ~33% of such patients (~300,000 new cases per year worldwide) will eventually develop anti-estrogen-resistant breast cancer that is metastatic or locally advanced; at this stage, the disease is almost never cured using available therapies and is uniformly fatal. Therefore, more effective treatment early in the course of disease (i.e., in the adjuvant setting, shortly after surgical removal of a tumor) has huge potential to prevent cancer regrowth.~Most often, ER+ breast cancers re-emerge in the years after the end of the standard five-year anti-estrogen treatment regimen (called 'late recurrence'). Recent data indicate that continued anti-estrogen therapy in patients who remain disease-free after five years of anti-estrogen therapy modestly prevents cancer recurrence. However, tumor cells are detectable in bone marrow of patients who are disease-free. Thus, anti-estrogen therapy in disease-free patients likely suppresses the growth of undetectable tumor cells, keeping them in a clinically dormant state (i.e., undetectable by standard clinical methods). Little is known about how such dormant cancer cells survive. This clinical study will help identify the signaling pathways essential for the survival of clinically dormant ER+ breast cancer cells to enable the development of more effective therapies to eradicate such cells and prevent cancer recurrence.
This is a single-arm, open-label study testing the effects of neoadjuvant therapy with the aromatase inhibitor letrozole in post-menopausal women with Stage I-III ER+, HER2- breast cancer. Eligible subjects will be treated with letrozole therapy for 4 to 12 weeks prior to surgical resection of the tumor. Tumor specimens obtained at baseline (diagnostic biopsy) and at surgery (surgical specimen) will be compared using molecular analyses. A subset of subjects will be asked to provide an optional research tumor biopsy prior to treatment for molecular analysis.