Letrozole in Treating Postmenopausal Women With Ductal Carcinoma in Situ

Treatment with letrozole begins within 21 days of registration, and only after notification has been received from the UCSF Breast MRI Research Laboratory that the baseline MRI is acceptable. Protocol therapy will consist of 6 months of letrozole, administered orally at a dose of 2.5 mg/day. Patients will have a MRI for disease evaluation at months 3 and 6. All patients will continue to take study drug until the day prior to surgery, whether at month 3 or at month 6 or may stop if they experience unacceptable toxicity. It is expected that decisions regarding any adjuvant treatment (eg, radiation and hormonal therapy) will be made individually based on the best practice guidelines, using informed and shared decision making between patient and provider. The primary and secondary objectives are provided below. Primary objective: 1\. To estimate the mean change in MRI tumor volume from pretreatment to completion of preoperative endocrine therapy in estrogen receptor-positive (ER+) ductal carcinoma in situ (DCIS), as well as to determine whether 3-month change in volume correlates with 6-month change. Secondary objectives: 1. To assess radiographic-pathologic correlation between MRI findings and histopathology, including the prevalence of occult invasive cancer in patients undergoing neoadjuvant endocrine therapy for DCIS. 2. To compare changes in MRI maximum lesion diameter and mammographic extent at baseline and following treatment. These are two additional radiographic parameters which may also biological response to therapy. 3. To determine practice patterns of adjuvant hormonal and radiation therapy in patients who complete neoadjuvant letrozole therapy for DCIS. 4. To determine whether Ki67 is reduced with neoadjuvant letrozole treatment for DCIS, and to compare the reduction in proliferation between radiographic responders and non-responders. 5. To identify baseline IHC and expression biomarkers predictive of response to treatment, with response determined by extent of Ki67 reduction. Subsets showing the greatest reduction in Ki67 would be the most likely candidates for non-operative treatment in future studies. 6. To examine whether germline polymorphisms are associated with clinical endpoints, including treatment-related toxicity or efficacy outcomes, or with expression of biomarkers in serum or tumor. 7. To assess quality-of-life and musculoskeletal symptoms associated with neoadjuvant letrozole for ER positive DCIS. Patients will be followed up to 6 months post-surgery.