Women with metastatic breast cancer who are completing planned course of chemotherapy with planned treatment break

On stable hormone therapy for at least 2 months are also eligible for the study

Estimated survival of at least 3 months

No platelet inhibitor therapy within 1 month of study entry

Platelets ≥ 100,000

Coagulation screening tests within normal range (INR between 0.81 and 1.20)

Normal kidney and liver function as defined by:

* Aspartate aminotransferase(AST)/serum glutamic oxaloacetic transaminase (SGOT))/alanine aminotransferase(ALT) ≤ 2 x Institutional Normal

* Creatinine ≤ 2 x Institutional Normal

Able to provide signed, informed consent.

A Study of the Effects of Inhibiting Platelet Function on Circulating Cancer Cells in Breast Cancer Patients