Study of Breast Cancer Prevention by Letrozole in High Risk Women

Inclusion Criteria:

- Post-menopausal women at high risk for development of breast cancer

- On a stable dose of hormone replacement therapy

- have cytomophologic evidence of hyperplasia +/- atypia and Ki-67 expression >1.5% in
benign breast epithelial cells acquired by RPFNA

- Serum level of 25-OH vitamin D of at least 30 ng/ml prior to study entry

- Willing to have a repeat RPFNA and mammogram at 6 months and 12 months (if
participating in the open label portion of the study) following initiation of study
drug

Exclusion Criteria:

- Prior history of osteoporosis or osteoporotic fracture.

- Prior history of invasive breast cancer or other invasive cancer within five years
from date of study entry.

- Current and chronic use of COX-2 specific inhibitors or NSAIDs

- Receiving treatment for rheumatoid arthritis or fibromyalgia

- Current history of poorly controlled migraines or perimenopausal symptoms

- Currently receiving other investigational agents.

- Receipt of more than 6 months of an aromatase inhibitor (anastrozole, exemestane,
letrozole, etc.) at any time in the past.