Research studies have shown a strong association between cancer and blood clots in the veins (also known as deep vein thrombosis). These blood clots can flow to the lungs (pulmonary embolism) which in severe cases may be life threatening. Studies have demonstrated that increases in microparticles may contribute to the development of deep vein thrombosis in cancer patients. The purpose of this research study is to see if rosuvastatin lowers the number of tissue factor bearing microparticles in the blood (TFMP). TFMP are small particles that are generated from different types of blood cells in the body. In people who have cancer, TFMP are thought to be generated from cancer cells and may represent a risk factor for deep vein thrombosis.

• Since no one knows which of the study options are best, participants will be "randomized" into the following study groups: Group 1 (regular dose of rosuvastatin) or Group 2 (higher dose of rosuvastatin).
• Participants will take 1 pill of rosuvastatin every day for 4 weeks. Each 4 week period is called a cycle.
• Participants will have a physical exam at baseline, on day 1 of starting rosuvastatin, and 2 month visits. Laboratory tests will be taken at baseline, on day 1 of starting rosuvastatin, 6 weeks and 2 months.

Inclusion Criteria:

• Metastatic adenocarcinoma of the breast (Stage IV)
• Actively receiving endocrine therapy for at least 6 weeks (with or without HER2 therapy)
• Minimum age 18 years
• ECOG Performance status of 0, 1 or 2
• Normal organ and marrow function as defined in the protocol

Exclusion Criteria:

• Participants may not be receiving any other study agents
• Actively receiving chemotherapy (exclusive of hormonal or HER2 therapy ) within last 5 weeks
• Any statin therapy within the last 3 weeks
• Asian decent (including Filipino, Chinese, Japanese, Korean, Vietnamese or Asian-Indian origin)
• Concomitant use of the following drugs: cyclosporine, fibrates, niacin, gemfibrozil, ketaconazole, spironolactone, cimetidine, warfarin, erythromycin, or protease inhibitors
• Conditions predisposing to renal failure secondary to rhabdomyolysis
• Recent history of heavy alcohol use as judged by the treating physician
• Known to be pregnant (testing not required) or nursing
• History of rhabdomyolysis on statin therapy
• Known history of Hepatitis C or active hepatitis B infection (baseline testing not required)
• Uncontrolled intercurrent illness including, but not limited to ongoing or active infection, hepatitis, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements

The analysis of dataset is comprised of all evaluable patients.

Assessed during the 4 weeks therapy