Letrozole in Post-Menopausal Patients With Operable Hormone-Sensitive Breast Cancer

Patients will receive a prescription for letrozole to be taken orally at a dose of 2.5 mg/day for 7-30 days to allow for variations in surgical scheduling. Patients are to undergo surgical resection of their tumor the day after the last dose of letrozole. Post-treatment tumor biopsies (a goal of 4-6 cores) will be obtained following 7-30 days of letrozole treatment on the day of surgery. Frozen AND formalin fixed core biopsies will be obtained whenever possible. The tissue will be used for study-specific assays as well as routine histopathology. Post-treatment core needle biopsy tissue will be obtained, whenever possible, by the surgeon intraoperatively at the time of routine surgical resection. A formalin-fixed paraffin embedded tumor block from the patient's surgical resection is also requested. This block will be used for a subset of the correlative studies if no tumor is obtained by the post treatment core biopsies. This block will be returned to pathology promptly after the correlative studies are completed. Surgical treatment (total mastectomy or segmental resection with lymph node evaluation if clinically indicated) will occur the day after completion of therapy. The primary lesion obtained at the time of the definitive surgical procedure (partial or total mastectomy) will be sent for standard of care histopathologic analysis; wherever possible intra-opearative cores from the central portion of the tumor will be obtained for study-specific assays. All specimens will be handled according to established institutional guidelines to maintain the accuracy of the analysis of tumor size and margin status. Following standard of care histopathologic analysis, additional paraffin-embedded sections will be submitted at a later time to the Simmons Cancer Tissue Core to determine tumor proliferation with Ki67 (MIB1Ab, Dako Cytomation) IHC. These tests are of no clinical utility and will be done for research purposes only. Frozen cores and/or peels from the formalin-fixed paraffin-embedded (FFPE) tumor blocks from the surgical specimen will be selected and/or macrodissected - when needed - based on ≥20% tumor cellularity as assessed by Dr. Sahoo, expert breast pathologist in the trial. These will be sent to Dr. Carlos Arteaga's laboratory for further testing.