Analysis of Letrozole in Patients With Operable Hormone Receptor Positive, HER2 Negative Breast Cancer

Inclusion Criteria:

• Postmenopausal and suitable to receive aromatase inhibitor as per physician'sdiscretion

• Histologically confirmed un-resected operable invasive adenocarcinoma of the breast ≥ 0.5 cm with estrogen receptor (ER) and/or progesterone receptor (PR) positive ≥ 10%, and no human epidermal growth factor receptor 2 (HER2) amplification oroverexpression

• Patients must not have received any prior chemotherapy, radiation therapy, orendocrine therapy for their current breast cancer. Patients who received tamoxifenor raloxifene or another agent for prevention of breast cancer may be included

• Willing and able to provide research tissue samples

• Willing and able to provide research blood samples

Exclusion Criteria:

• Immunocompromised patients including patients known to be human immunodeficiencyvirus (HIV) positive or those on chronic steroids

• NOTE: Must be off systemic steroids at least 14 days prior to pre-registration.However, topical steroids, inhalants or steroid eye drops are permitted

• Known history of active autoimmune disease that has required systemic treatmentwithin =< 30 days (i.e., with use of disease modifying agents, corticosteroids, orimmunosuppressive drugs) prior to pre-registration

• NOTE: Replacement therapy (e.g., thyroxine, insulin, or physiologiccorticosteroid replacement therapy for adrenal or pituitary insufficiency) isnot considered a form of systemic treatment. Patients with vitiligo, Gravesdisease, or psoriasis not requiring systemic treatment within the past 30 daysare not excluded. Patients with Celiac disease controlled with dietmodification are not excluded