Pharmacogenetics of Anastrozole in Postmenopausal Women With Estrogen Receptor-Positive and/or Progesterone Receptor-Positive Stage I, Stage II, or Stage III Breast Cancer

RATIONALE: Studying samples of blood in the laboratory from patients with cancer receiving anastrozole may help doctors learn more about changes that occur in DNA and identify biomarkers related to cancer. It may also help doctors learn more about how anastrozole works in the body. PURPOSE: This research study is looking at the pharmacogenetics of anastrozole in postmenopausal women with estrogen receptor-positive (ER+) and/or progesterone receptor-positive (PR+) stage I, stage II, or stage III breast cancer.