The Effect of Aspirin on Angiogenesis Proteins in Women on Tamoxifen Therapy

Inclusion Criteria: * Histologically or cytologically proven breast cancer * Pre or post-menopausal * Age \>18 * Completed adjuvant non-hormonal therapy \>30 days prior to initiation of study (surgery and/or chemotherapy and/or radiation therapy) * Platelet count and hemoglobin within normal ranges for local lab within 30 days of initiation of study therapy * Receiving tamoxifen therapy for at least 90 days prior to initiation of study therapy, and is expected to continue that therapy for the duration of the study (75 days) Exclusion Criteria: * Chemotherapy, radiation therapy or surgery within 30 days of study therapy * Current use of aspirin, anti-platelet or anti-coagulation agents on a continuous basis * Prior history of gastrointestinal or central nervous system bleeding, or documented or self-reported blood in stools or bright red blood per rectum