GCC 1366 is a prospective randomized window trial to evaluate the anti-proliferative response
      in obese and overweight breast cancer patients treated with neoadjuvant non-steroidal
      aromatase inhibitors. Post-menopausal women over the age of 18 years with estrogen receptor
      positive Her 2 neu negative stage II-III breast cancer are eligible. Participants will be
      randomized according to BMI to neoadjuvant treatment with Arimidex or Letrozole.

      A total of 90 patients will be enrolled with 15 patients in each cohort below.

        -  Cohort 1: Patients with BMI < 25.0 kg/m2 treating with anastrozole

        -  Cohort 2: Patients with BMI ≥ 25.0-29.9 kg/m2 treating with anastrozole

        -  Cohort 3: Patients with BMI ≥ 30 kg/m2 treating with anastrozole

        -  Cohort 4: Patients with BMI < 25.0 kg/m2 treating with letrozole

        -  Cohort 5: Patients with BMI ≥ 25.0-29.9 kg/m2 treating with letrozole

        -  Cohort 6: Patients with BMI ≥ 30 kg/m2 treating with letrozole

      Based on the patients' calculated BMI, patients in each BMI category (normal, overweight, and
      obese) will be enrolled in the different cohorts as described above. The first 15 patients in
      each BMI category will be treated with anastrozole. After completion of enrollment in cohorts
      1, 2, and 3, subsequent patients will be treated with letrozole in cohorts 4, 5, and 6.

      Anastrozole 1 mg or Letrozole 2.5 mg oral daily will be administered and continued for a
      minimum of 14 days and a maximum of 28 days (2-4 weeks). Surgery will be performed between
      weeks 2-3 of treatment unless there are compelling medical or personal reasons that prevent a
      patient from having surgery during this time. In those cases, patients may continue
      anastrozole or letrozole up to 4 weeks before surgery. Surgery should be performed within 36
      hours of the last dose of anastrozole or letrozole.

      Tumor tissue that is obtained for diagnosis or to assess response to initial AI therapy will
      be utilized for correlative studies. A patient may be continued on anastrozole or letrozole
      beyond 4 weeks (up to 18 weeks) if in the opinion of the treating physician, the patient will
      benefit from extended endocrine therapy. In this context, patients will have a core needle
      biopsy performed at 2-4 weeks after treatment to assess Ki67 response to AI therapy. Patients
      with an appropriate response to treatment as determined by a decrease in Ki67 levels (≤10%)
      will be continued on AI treatment. Patients without an appropriate decrease in Ki67 levels
      will be recommended to have immediate surgery or a switch to neoadjuvant chemotherapy if
      desired by the patient and treating physician.

      Patients on extended AI neoadjuvant treatment having core biopsy at 2-4 weeks for Ki67
      determination for clinical decision making will be approached and consented for additional
      research tissues to be taken at the same time as the biopsy for Ki67 determination. Blood
      samples will be collected prior to starting treatment and within 3 days or on the day of
      surgery. Additional blood samples will be obtained as clinically necessary.

      Clinical assessment will be performed prior to enrollment and within 3 days or on the day of
      surgery. For patients who continue neoadjuvant endocrine therapy past 4 weeks, clinical
      assessment will be performed at the time of clinical biopsy and every 4-6 weeks thereafter.
      For clinical evidence of progression, patients will be offered immediate surgery or switch to
      neoadjuvant chemotherapy at the discretion of the treating physician.

      Radiological assessment including mammogram, ultrasound, and breast MRI will be performed as
      per standard of care.

      Patients will be followed for 30 days on study after the last dose of anastrozole or
      letrozole prior to surgery. For patients who receive extended neoadjuvant therapy with
      anastrozole or letrozole and for patients who receive other primary treatment after
      anastrozole or letrozole administration prior to surgery, patients will be followed for 30
      days on study after the last dose of anastrozole or letrozole. Patients continuing to
      experience adverse events attributable to anastrozole or letrozole will be followed as needed
      until resolution or stabilization of the adverse events. Patients who are either found to be
      ineligible or refuse to start treatment after consenting will not be followed and will be
      replaced. Their information will not be collected. After 30 days after the last dose of
      anastrozole or letrozole, if there are no continuing adverse events attributable to
      treatment, patients will be off study.